SMTPD(8)

📦
version 3.10.14 · 4 versions
, in fedora 43, fedora 44

💌 SMTPD(8) — Postfix SMTP server

System Manager's Manual · the smtpd page, bestie edition 🦋

okay so you opened the manual for smtpd and it's giving a lot, but honestly? she's iconic and we're gonna go through her together. grab a strawberry drink 🍓 and let's go.

✨ NAME ✨

smtpd — the Postfix SMTP server 💅

✨ SYNOPSIS ✨

smtpd [generic Postfix daemon options]

sendmail -bs

✨ DESCRIPTION ✨

so the SMTP server accepts network connection requests and then does zero or more SMTP transactions per connection. every message she receives gets piped through the cleanup(8) daemon, and lands in the incoming queue as one single queue file. for this mode of operation, the program expects to be run from the master(8) process manager. periodt.

alternatively, the SMTP server can run in stand-alone mode 🧚 — traditionally you get that with "sendmail -bs". when the SMTP server runs stand-alone with non $mail_owner privileges, it receives mail even while the mail system is not running, deposits messages directly into the maildrop queue, and disables the SMTP server's access policies. and as of Postfix version 2.3, the SMTP server refuses to receive mail from the network when it runs with non $mail_owner privileges. no cap, she will not do it.

the SMTP server implements a whole variety of policies for connection requests, and for parameters given to HELO, ETRN, MAIL FROM, VRFY and RCPT TO commands. they're all detailed below and in the main.cf configuration file. 💖

🔒 SECURITY 🔒

the SMTP server is moderately security-sensitive. she talks to SMTP clients and to DNS servers on the network. the SMTP server can be run chrooted at fixed low privilege. 🛡️

📜 STANDARDS 📜

she speaks fluent RFC, bestie. all of these:

🩺 DIAGNOSTICS 🩺

problems and transactions get logged to syslogd(8) or postlogd(8). 📝

depending on the setting of the notify_classes parameter, the postmaster gets notified of bounces, protocol problems, policy violations, and of other trouble. she will tell on you (lovingly). 💀

⚙️ CONFIGURATION PARAMETERS ⚙️

changes to main.cf are picked up automatically, because smtpd(8) processes run for only a limited amount of time. use the command postfix reload to speed up a change. 🏃♀️💨

the text below provides only a parameter summary. see postconf(5) for more details including examples. iykyk.

🧩 COMPATIBILITY CONTROLS 🧩

the following parameters work around implementation errors in other software, and/or allow you to override standards in order to prevent undesirable use. bestie behavior tbh

  • broken_sasl_auth_clients (no) — enable interoperability with remote SMTP clients that implement an obsolete version of the AUTH command (RFC 4954).
  • disable_vrfy_command (no) — disable the SMTP VRFY command.
  • smtpd_noop_commands (empty) — list of commands that the Postfix SMTP server replies to with "250 Ok", without doing any syntax checks and without changing state.
  • strict_rfc821_envelopes (no) — require that addresses received in SMTP MAIL FROM and RCPT TO commands are enclosed with <>, and that those addresses do not contain RFC 822 style comments or phrases.

Available in Postfix version 2.1 and later:

  • smtpd_reject_unlisted_sender (no) — request that the Postfix SMTP server rejects mail from unknown sender addresses, even when no explicit reject_unlisted_sender access restriction is specified.
  • smtpd_sasl_exceptions_networks (empty) — what remote SMTP clients the Postfix SMTP server will not offer AUTH support to.

Available in Postfix version 2.2 and later:

  • smtpd_discard_ehlo_keyword_address_maps (empty) — lookup tables, indexed by the remote SMTP client address, with case insensitive lists of EHLO keywords (pipelining, starttls, auth, etc.) that the Postfix SMTP server will not send in the EHLO response to a remote SMTP client.
  • smtpd_discard_ehlo_keywords (empty) — a case insensitive list of EHLO keywords (pipelining, starttls, auth, etc.) that the Postfix SMTP server will not send in the EHLO response to a remote SMTP client.
  • smtpd_delay_open_until_valid_rcpt (yes) — postpone the start of an SMTP mail transaction until a valid RCPT TO command is received.

Available in Postfix version 2.3 and later:

  • smtpd_tls_always_issue_session_ids (yes) — force the Postfix SMTP server to issue a TLS session id, even when TLS session caching is turned off (smtpd_tls_session_cache_database is empty).

Available in Postfix version 2.6 and later:

  • tcp_windowsize (0) — an optional workaround for routers that break TCP window scaling.

Available in Postfix version 2.7 and later:

  • smtpd_command_filter (empty) — a mechanism to transform commands from remote SMTP clients.

Available in Postfix version 2.9 - 3.6:

  • smtpd_per_record_deadline (normal: no, overload: yes) — change the behavior of the smtpd_timeout and smtpd_starttls_timeout time limits, from a time limit per read or write system call, to a time limit to send or receive a complete record (an SMTP command line, SMTP response line, SMTP message content line, or TLS protocol message).

Available in Postfix version 3.0 and later:

  • smtpd_dns_reply_filter (empty) — optional filter for Postfix SMTP server DNS lookup results.

Available in Postfix 3.5 and later:

  • info_log_address_format (external) — the email address form that will be used in non-debug logging (info, warning, etc.).

Available in Postfix version 3.6 and later:

  • smtpd_relay_before_recipient_restrictions (see postconf -d output) — evaluate smtpd_relay_restrictions before smtpd_recipient_restrictions.
  • known_tcp_ports (lmtp=24, smtp=25, smtps=submissions=465, submission=587) — optional setting that avoids lookups in the services(5) database.

Available in Postfix version 3.7 and later:

  • smtpd_per_request_deadline (normal: no, overload: yes) — change the behavior of the smtpd_timeout and smtpd_starttls_timeout time limits, from a time limit per plaintext or TLS read or write call, to a combined time limit for receiving a complete SMTP request and for sending a complete SMTP response.
  • smtpd_min_data_rate (500) — the minimum plaintext data transfer rate in bytes/second for DATA and BDAT requests, when deadlines are enabled with smtpd_per_request_deadline.

💌 ADDRESS REWRITING CONTROLS 💌

see the ADDRESS_REWRITING_README document for a detailed discussion of Postfix address rewriting. it's giving ✨glow up for addresses✨

  • receive_override_options (empty) — enable or disable recipient validation, built-in content filtering, or address mapping.

Available in Postfix version 2.2 and later:

  • local_header_rewrite_clients (permit_inet_interfaces) — rewrite or add message headers in mail from these clients, updating incomplete addresses with the domain name in $myorigin or $mydomain, and adding missing headers.

🧚 BEFORE-SMTPD PROXY AGENT 🧚

Available in Postfix version 2.10 and later:

  • smtpd_upstream_proxy_protocol (empty) — the name of the proxy protocol used by an optional before-smtpd proxy agent.
  • smtpd_upstream_proxy_timeout (5s) — the time limit for the proxy protocol specified with the smtpd_upstream_proxy_protocol parameter.

📤 AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS 📤

as of version 1.0, Postfix can be configured to send new mail to an external content filter AFTER the mail is queued. this content filter is expected to inject mail back into a (Postfix or other) MTA for further delivery. see the FILTER_README document for details. 🔍

  • content_filter (empty) — after the message is queued, send the entire message to the specified transport:destination.

📥 BEFORE QUEUE EXTERNAL CONTENT INSPECTION CONTROLS 📥

as of version 2.1, the Postfix SMTP server can be configured to send incoming mail to a real-time SMTP-based content filter BEFORE mail is queued. this content filter is expected to inject mail back into Postfix. see the SMTPD_PROXY_README document for details on how to configure and operate this feature. 🫶

  • smtpd_proxy_filter (empty) — the hostname and TCP port of the mail filtering proxy server.
  • smtpd_proxy_ehlo ($myhostname) — how the Postfix SMTP server announces itself to the proxy filter.
  • smtpd_proxy_options (empty) — list of options that control how the Postfix SMTP server communicates with a before-queue content filter.
  • smtpd_proxy_timeout (100s) — the time limit for connecting to a proxy filter and for sending or receiving information.

okay and that's just part 1, bestie — there is SO much more smtpd coming your way 💖 don't go anywhere ✨

✨ BEFORE QUEUE MILTER CONTROLS ✨

okay so bestie, as of version 2.3, Postfix is literally besties with the Sendmail version 8 Milter (mail filter) protocol. These content filters run outside Postfix (main character energy, fr fr). They can inspect the SMTP command stream and the message content, and can request modifications before mail is queued. For all the tea, see the MILTER_README document. 💅

  • smtpd_milters (empty) — The list of Milter (mail filter) apps that get to check out new mail coming in via the Postfix smtpd(8) server. 💌
  • milter_protocol (6) — The mail filter protocol version and optional protocol extensions for chatting with a Milter application. Heads up: before Postfix 2.6, the default was 2. 💀
  • milter_default_action (see postconf -d milter_default_action output) — The default action when a Milter (mail filter) response is MIA (like if your Postfix config is a mess or the Milter just ghosted you). 😭
  • milter_macro_daemon_name ($myhostname) — The {daemon_name} macro value for Milter (mail filter) applications. 🎀
  • milter_macro_v ($mail_name $mail_version) — The {v} macro value for Milter (mail filter) applications. 🌸
  • milter_connect_timeout (30s) — The time limit for connecting to a Milter (mail filter) application, and for negotiating protocol options. ⏳
  • milter_command_timeout (30s) — The time limit for sending an SMTP command to a Milter (mail filter) application, and for receiving the response. 📨
  • milter_content_timeout (300s) — The time limit for sending message content to a Milter (mail filter) application, and for receiving the response. 📦
  • milter_connect_macros (see postconf -d output) — The macros that get sent to Milter (mail filter) applications after an SMTP connection is done. 🔌
  • milter_helo_macros (see postconf -d output) — The macros that get sent to Milter (mail filter) applications after the SMTP HELO or EHLO command. 👋
  • milter_mail_macros (see postconf -d output) — The macros that get sent to Milter (mail filter) applications after the SMTP MAIL FROM command. 📧
  • milter_rcpt_macros (see postconf -d output) — The macros that get sent to Milter (mail filter) applications after the SMTP RCPT TO command. 📬
  • milter_data_macros (see postconf -d output) — The macros that get sent to version 4 or higher Milter (mail filter) applications after the SMTP DATA command. 🗂️
  • milter_unknown_command_macros (see postconf -d output) — The macros that get sent to version 3 or higher Milter (mail filter) applications after an unknown SMTP command. ❓
  • milter_end_of_header_macros (see postconf -d output) — The macros that get sent to Milter (mail filter) applications after the message header ends. 🏁
  • milter_end_of_data_macros (see postconf -d output) — The macros that get sent to Milter (mail filter) applications after the message end-of-data. 🔚

✨ Available in Postfix version 3.1 and later ✨

  • milter_macro_defaults (empty) — Optional list of name=value pairs that set default values for any macros Postfix might send to Milter applications. 🌟

✨ Available in Postfix version 3.2 and later ✨

  • smtpd_milter_maps (empty) — Lookup tables with Milter settings for each remote SMTP client IP address. 🗺️

✨ GENERAL CONTENT INSPECTION CONTROLS ✨

These parameters work for both built-in and external content filters. 👯

✨ Available in Postfix version 2.1 and later ✨

  • receive_override_options (empty) — Turn on or off recipient validation, built-in content filtering, or address mapping. 🎛️

✨ EXTERNAL CONTENT INSPECTION CONTROLS ✨

These parameters are for both before-queue and after-queue content filtering. 🔄

✨ Available in Postfix version 2.1 and later ✨

  • smtpd_authorized_xforward_hosts (empty) — Which remote SMTP clients get to use the XFORWARD feature. 🚀

✨ SASL AUTHENTICATION CONTROLS ✨

Postfix SASL support (RFC 4954) can be used to authenticate remote SMTP clients to the Postfix SMTP server, and to authenticate the Postfix SMTP client to a remote SMTP server. See the SASL_README document for details. 🔐

  • broken_sasl_auth_clients (no) — Enable interoperability with remote SMTP clients that implement an obsolete version of the AUTH command (RFC 4954). 🛠️
  • smtpd_sasl_auth_enable (no) — Turn on SASL authentication in the Postfix SMTP server. 🔓
  • smtpd_sasl_local_domain (empty) — The name of the Postfix SMTP server's local SASL authentication realm. 🏰
  • smtpd_sasl_security_options (noanonymous) — Postfix SMTP server SASL security options. As of Postfix 2.3, the available features depend on the SASL server implementation you pick with smtpd_sasl_type. 🛡️
  • smtpd_sender_login_maps (empty) — Optional lookup table with the SASL login names that own the envelope sender (MAIL FROM) addresses. 📇

✨ Available in Postfix version 2.1 and later ✨

  • smtpd_sasl_exceptions_networks (empty) — Which remote SMTP clients the Postfix SMTP server will not offer AUTH support to. 🚫

✨ Available in Postfix version 2.1 and 2.2 ✨

  • smtpd_sasl_application_name (smtpd) — The application name that the Postfix SMTP server uses for SASL server initialization. 📛

✨ Available in Postfix version 2.3 and later ✨

  • smtpd_sasl_authenticated_header (no) — Report the SASL authenticated user name in the smtpd(8) Received message header. 📝
  • smtpd_sasl_path (smtpd) — Implementation-specific info that the Postfix SMTP server passes to the SASL plug-in implementation chosen with smtpd_sasl_type. 🔌
  • smtpd_sasl_type (cyrus) — The SASL plug-in type that the Postfix SMTP server should use for authentication. 🔑

✨ Available in Postfix version 2.5 and later ✨

  • cyrus_sasl_config_path (empty) — Search path for Cyrus SASL application configuration files, currently used only to locate the $smtpd_sasl_path.conf file. 📂

✨ Available in Postfix version 2.11 and later ✨

  • smtpd_sasl_service (smtp) — The service name passed to the SASL plug-in selected with smtpd_sasl_type and smtpd_sasl_path. 🛎️

✨ Available in Postfix version 3.4 and later ✨

  • smtpd_sasl_response_limit (12288) — The maximum length of a SASL client's response to a server challenge. 📏

✨ Available in Postfix 3.6 and later ✨

  • smtpd_sasl_mechanism_filter (!external, static:rest) — If non-empty, a filter for the SASL mechanism names that the Postfix SMTP server will announce in the EHLO response. 🎯

✨ STARTTLS SUPPORT CONTROLS ✨

okay bestie, if you're tryna get the full tea on STARTTLS configuration, it's all in the TLS_README document. no cap, that's the required reading. 💅

  • smtpd_tls_security_level (empty) — the SMTP TLS security level for the Postfix SMTP server. when you set it to a non-empty value, it overrides those obsolete smtpd_use_tls and smtpd_enforce_tls parameters. it's giving main character energy, fr. 👑
  • smtpd_sasl_tls_security_options ($smtpd_sasl_security_options) — the SASL authentication security options that the Postfix SMTP server uses for TLS encrypted SMTP sessions. default is whatever $smtpd_sasl_security_options is. 🎀
  • smtpd_starttls_timeout (see 'postconf -d' output) — the time limit for Postfix SMTP server write and read operations during TLS startup and shutdown handshake procedures. default? run postconf -d to find out. ✨
  • smtpd_tls_CAfile (empty) — a file containing (PEM format) CA certificates of root CAs trusted to sign either remote SMTP client certificates or intermediate CA certificates. default empty. 💖
  • smtpd_tls_CApath (empty) — a directory containing (PEM format) CA certificates of root CAs trusted to sign either remote SMTP client certificates or intermediate CA certificates. default empty. 🦋
  • smtpd_tls_always_issue_session_ids (yes) — force the Postfix SMTP server to issue a TLS session id, even when TLS session caching is turned off (smtpd_tls_session_cache_database is empty). default yes. periodt. 💅
  • smtpd_tls_ask_ccert (no) — ask a remote SMTP client for a client certificate. default no. 🙈
  • smtpd_tls_auth_only (no) — when TLS encryption is optional in the Postfix SMTP server, don't announce or accept SASL authentication over unencrypted connections. default no. 🔥
  • smtpd_tls_ccert_verifydepth (9) — the verification depth for remote SMTP client certificates. default 9. 🌈
  • smtpd_tls_cert_file (empty) — file with the Postfix SMTP server RSA certificate in PEM format. default empty. 🎀
  • smtpd_tls_exclude_ciphers (empty) — list of ciphers or cipher types to exclude from the SMTP server cipher list at all TLS security levels. default empty. 💀
  • smtpd_tls_dcert_file (empty) — file with the Postfix SMTP server DSA certificate in PEM format. default empty. 🦋
  • smtpd_tls_dh1024_param_file (empty) — file with DH parameters that the Postfix SMTP server should use with non-export EDH ciphers. default empty. ✨
  • smtpd_tls_dh512_param_file (empty) — file with DH parameters that the Postfix SMTP server should use with export-grade EDH ciphers. default empty. 💖
  • smtpd_tls_dkey_file ($smtpd_tls_dcert_file) — file with the Postfix SMTP server DSA private key in PEM format. default is $smtpd_tls_dcert_file. 🔑
  • smtpd_tls_key_file ($smtpd_tls_cert_file) — file with the Postfix SMTP server RSA private key in PEM format. default is $smtpd_tls_cert_file. 💅
  • smtpd_tls_loglevel (0) — enable additional Postfix SMTP server logging of TLS activity. default 0. 📝
  • smtpd_tls_mandatory_ciphers (medium) — the minimum TLS cipher grade that the Postfix SMTP server will use with mandatory TLS encryption. default medium. 👑
  • smtpd_tls_mandatory_exclude_ciphers (empty) — additional list of ciphers or cipher types to exclude from the Postfix SMTP server cipher list at mandatory TLS security levels. default empty. 🚫
  • smtpd_tls_mandatory_protocols (see 'postconf -d' output) — TLS protocols accepted by the Postfix SMTP server with mandatory TLS encryption. default? postconf -d has the tea. ☕
  • smtpd_tls_received_header (no) — request that the Postfix SMTP server produces Received: message headers that include information about the protocol and cipher used, as well as the remote SMTP client CommonName and client certificate issuer CommonName. default no. 💌
  • smtpd_tls_req_ccert (no) — with mandatory TLS encryption, require a trusted remote SMTP client certificate in order to allow TLS connections to proceed. default no. 🔒
  • smtpd_tls_wrappermode (no) — run the Postfix SMTP server in TLS "wrapper" mode, instead of using the STARTTLS command. default no. 🎁
  • tls_daemon_random_bytes (32) — the number of pseudo-random bytes that an smtp(8) or smtpd(8) process requests from the tlsmgr(8) server in order to seed its internal pseudo random number generator (PRNG). default 32. 🎲
  • tls_high_cipherlist (see 'postconf -d' output) — the OpenSSL cipherlist for "high" grade ciphers. default? postconf -d. 🔥
  • tls_medium_cipherlist (see 'postconf -d' output) — the OpenSSL cipherlist for "medium" or higher grade ciphers. default? postconf -d. ✨
  • tls_null_cipherlist (eNULL:!aNULL) — the OpenSSL cipherlist for "NULL" grade ciphers that provide authentication without encryption. default eNULL:!aNULL. 💀

Available in Postfix version 2.3..3.7:

  • tls_low_cipherlist (see 'postconf -d' output) — the OpenSSL cipherlist for "low" or higher grade ciphers. default? postconf -d. 🌸
  • tls_export_cipherlist (see 'postconf -d' output) — the OpenSSL cipherlist for "export" or higher grade ciphers. default? postconf -d. 🧚

Available in Postfix version 2.5 and later:

  • smtpd_tls_fingerprint_digest (see 'postconf -d' output) — the message digest algorithm to construct remote SMTP client-certificate fingerprints or public key fingerprints (Postfix 2.9 and later) for check_ccert_access and permit_tls_clientcerts. default? postconf -d. 🔍

Available in Postfix version 2.6 and later:

  • smtpd_tls_protocols (see 'postconf -d' output) — TLS protocols accepted by the Postfix SMTP server with opportunistic TLS encryption. default? postconf -d. 🌈
  • smtpd_tls_ciphers (medium) — the minimum TLS cipher grade that the Postfix SMTP server will use with opportunistic TLS encryption. default medium. 💅
  • smtpd_tls_eccert_file (empty) — file with the Postfix SMTP server ECDSA certificate in PEM format. default empty. 🍓
  • smtpd_tls_eckey_file ($smtpd_tls_eccert_file) — file with the Postfix SMTP server ECDSA private key in PEM format. default $smtpd_tls_eccert_file. 🔑
  • smtpd_tls_eecdh_grade (see 'postconf -d' output) — the Postfix SMTP server security grade for ephemeral elliptic-curve Diffie-Hellman (EECDH) key exchange. default? postconf -d. 🛡️
  • tls_eecdh_strong_curve (prime256v1) — the elliptic curve used by the Postfix SMTP server for sensibly strong ephemeral ECDH key exchange. default prime256v1. 🌟
  • tls_eecdh_ultra_curve (secp384r1) — the elliptic curve used by the Postfix SMTP server for maximally strong ephemeral ECDH key exchange. default secp384r1. 💎

Available in Postfix version 2.8 and later:

  • tls_preempt_cipherlist (no) — with SSLv3 and later, use the Postfix SMTP server's cipher preference order instead of the remote client's cipher preference order. default no. 👑
  • tls_disable_workarounds (see 'postconf -d' output) — list or bit-mask of OpenSSL bug work-arounds to disable. default? postconf -d. 🐛

Available in Postfix version 2.11 and later:

  • tlsmgr_service_name (tlsmgr) — the name of the tlsmgr(8) service entry in master.cf. default tlsmgr. 📋

Available in Postfix version 3.0 and later:

  • tls_session_ticket_cipher (Postfix >= 3.0: aes-256-cbc, Postfix < 3.0: aes-128-cbc) — algorithm used to encrypt RFC5077 TLS session tickets. default: Postfix >= 3.0 uses aes-256-cbc, Postfix < 3.0 uses aes-128-cbc. 🎟️

Available in Postfix version 3.2 and later:

  • tls_eecdh_auto_curves (see 'postconf -d' output) — the prioritized list of elliptic curves, that should be enabled in the Postfix SMTP client and server. default? postconf -d. 📈

Available in Postfix version 3.4 and later:

  • smtpd_tls_chain_files (empty) — list of one or more PEM files, each holding one or more private keys directly followed by a corresponding certificate chain. default empty. 🔗
  • tls_server_sni_maps (empty) — optional lookup tables that map names received from remote SMTP clients via the TLS Server Name Indication (SNI) extension to the appropriate keys and certificate chains. default empty. 🗺️

Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:

  • tls_fast_shutdown_enable (yes) — a workaround for implementations that hang Postfix while shutting down a TLS session, until Postfix times out. default yes. ⏱️

Available in Postfix version 3.8 and later:

  • tls_ffdhe_auto_groups (see 'postconf -d' output) — the prioritized list of finite-field Diffie-Hellman ephemeral (FFDHE) key exchange groups supported by the Postfix SMTP client and server. default? postconf -d. 🧮

Available in Postfix 3.9, 3.8.1, 3.7.6, 3.6.10, 3.5.20 and later:

  • tls_config_file (default) — optional configuration file with baseline OpenSSL settings. default default. ⚙️
  • tls_config_name (empty) — the application name passed by Postfix to OpenSSL library initialization functions. default empty. 🏷️

Available in Postfix version 3.9 and later:

  • smtpd_tls_enable_rpk (no) — request that remote SMTP clients send an RFC7250 raw public key instead of an X.509 certificate, when asking for or requiring client authentication. default no. 🔑

🚫 OBSOLETE STARTTLS CONTROLS 🚫

okay so these config parameters are only here for compatibility with Postfix versions before 2.3. support for them is getting yeeted in a future release, so don't get too attached, bestie. 💀

  • smtpd_use_tls (no) — opportunistic TLS: announce STARTTLS support to remote SMTP clients, but do not require that clients use TLS encryption. default no. 🙈
  • smtpd_enforce_tls (no) — mandatory TLS: announce STARTTLS support to remote SMTP clients, and reject all plaintext commands except HELO, EHLO, XCLIENT, STARTTLS, NOOP, QUIT, and (Postfix >= 3.9) HELP. default no. 🔒
  • smtpd_tls_cipherlist (empty) — obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher list. default empty. 🗑️

🌍 SMTPUTF8 CONTROLS 🌍

preliminary SMTPUTF8 support is introduced with Postfix 3.0. it's giving international vibes, no cap. 🌐

  • smtputf8_enable (yes) — enable preliminary SMTPUTF8 support for the protocols described in RFC 6531, RFC 6532, and RFC 6533. default yes. ✨
  • strict_smtputf8 (no) — enable stricter enforcement of the SMTPUTF8 protocol. default no. 😤
  • smtputf8_autodetect_classes (sendmail, verify) — detect that a message requires SMTPUTF8 support for the specified mail origin classes. default sendmail, verify. 🔍

Available in Postfix version 3.2 and later:

  • enable_idna2003_compatibility (no) — enable 'transitional' compatibility between IDNA2003 and IDNA2008, when converting UTF-8 domain names to/from the ASCII form that is used for DNS lookups. default no. 🌐

✨ VERP SUPPORT CONTROLS ✨

ok so bestie, VERP style delivery is a whole vibe 💅 — with it, every single recipient of a message gets their own customized copy of the message, with their own recipient address encoded in the envelope sender address. it's giving personalized, no cap 🎀. the VERP_README file spills all the configuration and operation details of Postfix support for variable envelope return path addresses. you ask for VERP style delivery with the SMTP XVERP command or with the "sendmail -V" command-line option, and it's been a thing since Postfix version 1.1 and later. iconic ✨

  • default_verp_delimiters (+=) — the two default VERP delimiter characters. yes, just two, that's the whole job 🌸
  • verp_delimiter_filter (-=+) — the characters Postfix accepts as VERP delimiter characters on the Postfix sendmail(1) command line and in SMTP commands.

Available in Postfix version 1.1 and 2.0:

  • authorized_verp_clients ($mynetworks) — what remote SMTP clients are allowed to specify the XVERP command.

Available in Postfix version 2.1 and later:

  • smtpd_authorized_verp_clients ($authorized_verp_clients) — what remote SMTP clients are allowed to specify the XVERP command. (yeah it's the glow-up version of the one above, same energy, new name 🦋)

🔍 TROUBLE SHOOTING CONTROLS 🔍

the DEBUG_README document describes how to debug parts of the Postfix mail system 🧚. the methods vary from making the software log a lot of detail, to running some daemon processes under control of a call tracer or debugger. pick your fighter, bestie 💜

  • debug_peer_level (2) — the increment in verbose logging level when a nexthop destination, remote client or server name or network address matches a pattern given with the debug_peer_list parameter.
  • debug_peer_list (empty) — optional list of nexthop destination, remote client or server name or network address patterns that, if matched, cause the verbose logging level to increase by the amount specified in $debug_peer_level.
  • error_notice_recipient (postmaster) — the recipient of postmaster notifications about mail delivery problems that are caused by policy, resource, software or protocol errors. someone's gotta get the bad news 📬
  • internal_mail_filter_classes (empty) — what categories of Postfix-generated mail are subject to before-queue content inspection by non_smtpd_milters, header_checks and body_checks.
  • notify_classes (resource, software) — the list of error classes that are reported to the postmaster.
  • smtpd_reject_footer (empty) — optional information that is appended after each Postfix SMTP server 4XX or 5XX response.
  • soft_bounce (no) — safety net to keep mail queued that would otherwise be returned to the sender. literal safety net, protect it at all costs 🫶

Available in Postfix version 2.1 and later:

  • smtpd_authorized_xclient_hosts (empty) — what remote SMTP clients are allowed to use the XCLIENT feature.

Available in Postfix version 2.10 and later:

  • smtpd_log_access_permit_actions (empty) — enable logging of the named "permit" actions in SMTP server access lists (by default, the SMTP server logs "reject" actions but not "permit" actions). so rude of it to keep the permits quiet, honestly 😭

👀 KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS 👀

as of Postfix version 2.0, the SMTP server rejects mail for unknown recipients. this prevents the mail queue from clogging up with undeliverable MAILER-DAEMON messages 🚫📭. additional info on this topic lives in the LOCAL_RECIPIENT_README and ADDRESS_CLASS_README documents — go read them, they're worth it, fr fr.

  • show_user_unknown_table_name (yes) — display the name of the recipient table in the "User unknown" responses.
  • canonical_maps (empty) — optional address mapping lookup tables for message headers and envelopes.
  • recipient_canonical_maps (empty) — optional address mapping lookup tables for envelope and header recipient addresses.
  • sender_canonical_maps (empty) — optional address mapping lookup tables for envelope and header sender addresses.

💖 Parameters concerning known/unknown local recipients 💖

  • mydestination ($myhostname, localhost.$mydomain, localhost) — the list of domains that are delivered via the $local_transport mail delivery transport.
  • inet_interfaces (all) — the local network interface addresses that this mail system receives mail on.
  • proxy_interfaces (empty) — the remote network interface addresses that this mail system receives mail on by way of a proxy or network address translation unit.
  • inet_protocols (see 'postconf -d' output) — the Internet protocols Postfix will attempt to use when making or accepting connections.
  • local_recipient_maps (proxy:unix:passwd.byname $alias_maps) — lookup tables with all names or addresses of valid local recipients.
  • unknown_local_recipient_reject_code (550) — the numerical Postfix SMTP server response code when a recipient address is local, and $local_recipient_maps specifies a list of lookup tables that does not match the recipient.

🌈 Parameters concerning known/unknown recipients of relay destinations 🌈

  • relay_domains (Postfix >= 3.0: empty, Postfix < 3.0: $mydestination) — what destination domains (and subdomains thereof) this system will relay mail to.
  • relay_recipient_maps (empty) — optional lookup tables with all valid addresses in the domains that match $relay_domains.
  • unknown_relay_recipient_reject_code (550) — the numerical Postfix SMTP server reply code when a recipient address matches $relay_domains, and relay_recipient_maps specifies a list of lookup tables that does not match the recipient address.

🦋 Parameters concerning known/unknown recipients in virtual alias domains 🦋

  • virtual_alias_domains ($virtual_alias_maps) — Postfix is the final destination for the specified list of virtual alias domains, that is, domains for which all addresses are aliased to addresses in other local or remote domains.
  • virtual_alias_maps ($virtual_maps) — optional lookup tables that are often searched with a full email address (including domain) and that apply to all recipients: local(8), virtual, and remote; this is unlike alias_maps that are only searched with an email address localpart (no domain) and that apply only to local(8) recipients. the way these two are not the same thing is so important, do not mix them up bestie 🙈
  • unknown_virtual_alias_reject_code (550) — the Postfix SMTP server reply code when a recipient address matches $virtual_alias_domains, and $virtual_alias_maps specifies a list of lookup tables that does not match the recipient address.

🎀 Parameters concerning known/unknown recipients in virtual mailbox domains 🎀

  • virtual_mailbox_domains ($virtual_mailbox_maps) — Postfix is the final destination for the specified list of domains; mail is delivered via the $virtual_transport mail delivery transport.
  • virtual_mailbox_maps (empty) — optional lookup tables with all valid addresses in the domains that match $virtual_mailbox_domains.
  • unknown_virtual_mailbox_reject_code (550) — the Postfix SMTP server reply code when a recipient address matches $virtual_mailbox_domains, and $virtual_mailbox_maps specifies a list of lookup tables that does not match the recipient address.

✨ RESOURCE AND RATE CONTROLS ✨

Okay bestie, this is where Postfix SMTPD learns ✨boundaries✨. These params cap how much of your machine the SMTP server is allowed to eat, and how fast any one client can spam requests at it. Very "know your worth" of it, honestly. 💅

  • line_length_limit (default 2048) — when stuff comes in, long lines get chopped up into little pieces no bigger than this length. When it goes back out on delivery, those long lines get stitched back together like nothing happened. 🪄
  • queue_minfree (default 0) — the bare minimum free space (in bytes) that the queue file system needs to have before it'll even accept mail. Zero means "idk, we're not checking", basically.
  • message_size_limit (default 10240000) — the biggest a message can be in bytes, and yeah that count includes the envelope info too. 👑
  • smtpd_recipient_limit (default 1000) — how many recipients the Postfix SMTP server will accept per single message delivery request. The group chat max member count, fr.
  • smtpd_timeout (default: normal 300s, overload 10s) — two jobs in one, iconic. When the server wants to send an SMTP response, this is how long it waits for the underlying network write to finish. And when it wants to receive an SMTP client request, this is how long it waits for the underlying network read to finish.
  • smtpd_history_flush_threshold (default 100) — the max number of lines allowed in the SMTP server command history before it gets flushed on receipt of EHLO, RSET, or end of DATA. Memory hygiene, we love to see it. 🧼

Available in Postfix version 2.3 and later:

  • smtpd_peername_lookup (default yes) — try to look up the remote SMTP client hostname, then double check that the name actually matches the client IP address. No catfishing allowed. 🙅

The per-SMTP-client connection count and request rate limits get done in co-operation with the anvil(8) service, and they exist in Postfix version 2.2 and later. 🫶

  • smtpd_client_connection_count_limit (default 50) — how many simultaneous connections any one client is allowed to open to this service.
  • smtpd_client_connection_rate_limit (default 0) — the max number of connection attempts any client gets to make to this service per time unit.
  • smtpd_client_message_rate_limit (default 0) — the max number of message delivery requests any client can make per time unit, and it does not care whether Postfix actually accepts those messages. Counted regardless, periodt.
  • smtpd_client_recipient_rate_limit (default 0) — the max number of recipient addresses any client can send to this service per time unit, again regardless of whether Postfix actually accepts those recipients.
  • smtpd_client_event_limit_exceptions (default $mynetworks) — the clients that get excluded from all the smtpd_client_*_count/rate_limit restrictions. The VIP list. 💖

Available in Postfix version 2.3 and later:

  • smtpd_client_new_tls_session_rate_limit (default 0) — the max number of new (aka uncached) TLS sessions a remote SMTP client is allowed to negotiate with this service per time unit. Fresh handshakes only, no reusing. 🦋

Available in Postfix version 2.9 - 3.6:

  • smtpd_per_record_deadline (default: normal no, overload yes) — this switches up how smtpd_timeout and smtpd_starttls_timeout behave. Instead of being a time limit per read or write system call, it becomes a time limit for sending or receiving one complete record — meaning an SMTP command line, an SMTP response line, an SMTP message content line, or a TLS protocol message.

Available in Postfix version 3.1 and later:

  • smtpd_client_auth_rate_limit (default 0) — the max number of AUTH commands any client can send to this service per time unit, regardless of whether Postfix actually accepts those commands.

Available in Postfix version 3.7 and later:

  • smtpd_per_request_deadline (default: normal no, overload yes) — changes how smtpd_timeout and smtpd_starttls_timeout work, from a time limit per plaintext or TLS read or write call, into one combined time limit for receiving a complete SMTP request and sending a complete SMTP response. Two birds, one deadline. 🎯
  • smtpd_min_data_rate (default 500) — the minimum plaintext data transfer rate in bytes/second for DATA and BDAT requests, but only when deadlines are enabled with smtpd_per_request_deadline.
  • header_from_format (default standard) — the format of the Postfix-generated From: header.

Available in Postfix version 3.8 and later:

  • smtpd_client_ipv4_prefix_length (default 32) — aggregates the smtpd_client_*_count and smtpd_client_*_rate statistics by IPv4 network blocks with the specified network prefix.
  • smtpd_client_ipv6_prefix_length (default 84) — same energy, but for IPv6 network blocks. 🌈

Available in Postfix 3.9, 3.8.1, 3.7.6, 3.6.10, 3.5.20 and later:

  • smtpd_forbid_unauth_pipelining (default: Postfix >= 3.9: yes) — disconnects remote SMTP clients that violate RFC 2920 (or 5321) command pipelining constraints. Breaking the rules = you're out. 💀

Available in Postfix 3.9, 3.8.4, 3.7.9, 3.6.13, 3.5.23 and later:

  • smtpd_forbid_bare_newline (default: Postfix >= 3.9: normalize) — rejects or restricts input lines from an SMTP client that end in <LF> instead of the standard <CR><LF>. Bare newlines are NOT it.
  • smtpd_forbid_bare_newline_exclusions (default $mynetworks) — excludes the specified clients from smtpd_forbid_bare_newline enforcement. Your faves get a pass. 🫶

Available in Postfix 3.9, 3.8.5, 3.7.10, 3.6.14, 3.5.24 and later:

  • smtpd_forbid_bare_newline_reject_code (default 550) — the numerical Postfix SMTP server response code used when rejecting a request with "smtpd_forbid_bare_newline = reject".

🌸 TARPIT CONTROLS 🌸

So when a remote SMTP client starts making errors, the Postfix SMTP server can insert delays before responding. Think of it as the world's politest "oh... okay... take your time...". It helps slow down run-away software. 🐌

The whole thing is governed by an error counter that counts the number of errors within an SMTP session that a client makes without delivering mail.

  • smtpd_error_sleep_time (default 1s) — with Postfix version 2.1 and later: the SMTP server response delay applied after a client has made more than $smtpd_soft_error_limit errors, and fewer than $smtpd_hard_error_limit errors, without delivering mail.
  • smtpd_soft_error_limit (default 10) — the number of errors a remote SMTP client gets to make without delivering mail before the Postfix SMTP server starts slowing down all its responses. The gentle warning era.
  • smtpd_hard_error_limit (default: normal 20, overload 1) — the max number of errors a remote SMTP client is allowed to make without delivering mail. Hit it and we're done here. 😤
  • smtpd_junk_command_limit (default: normal 100, overload 1) — the number of junk commands (NOOP, VRFY, ETRN or RSET) a remote SMTP client can send before the Postfix SMTP server starts bumping the error counter on every single junk command. Stop playing. 🙈

Available in Postfix version 2.1 and later:

  • smtpd_recipient_overshoot_limit (default 1000) — the number of recipients a remote SMTP client can send in excess of the limit set with $smtpd_recipient_limit, before the Postfix SMTP server increments the per-session error count for each excess recipient.

👑 ACCESS POLICY DELEGATION CONTROLS 👑

As of version 2.1, Postfix can be configured to delegate access policy decisions to an external server running outside Postfix. Go read the file SMTPD_POLICY_README for the full tea. ☕

  • smtpd_policy_service_max_idle (default 300s) — the time after which an idle SMTPD policy service connection gets closed.
  • smtpd_policy_service_max_ttl (default 1000s) — the time after which an active SMTPD policy service connection gets closed.
  • smtpd_policy_service_timeout (default 100s) — the time limit for connecting to, writing to, or receiving from a delegated SMTPD policy server.

Available in Postfix version 3.0 and later:

  • smtpd_policy_service_default_action (default 451 4.3.5 Server configuration problem) — the default action taken when an SMTPD policy service request fails. Not the vibe you want to be seeing, but at least it's defined.
  • smtpd_policy_service_request_limit (default 0) — the max number of requests per SMTPD policy service connection, or zero for no limit.
  • smtpd_policy_service_try_limit (default 2) — the max number of attempts to send an SMTPD policy service request before giving up.
  • smtpd_policy_service_retry_delay (default 1s) — the delay between attempts to resend a failed SMTPD policy service request.

Available in Postfix version 3.1 and later:

  • smtpd_policy_service_policy_context (default empty) — optional info that the Postfix SMTP server specifies in the "policy_context" attribute of a policy service request. Originally this existed so multiple check_policy_service clients could share the same service endpoint. Sharing is caring, bestie. 💜

🎀 ACCESS CONTROLS 🎀

ok bestie, before we dive into the ~fifty~ parameters, know this: the SMTPD_ACCESS_README document is your girl. It's the whole intro to literally every access control feature this SMTP server has, so go read her if you want the full picture. ✨

  • smtpd_delay_reject (default: yes) — wait until the RCPT TO command before you evaluate $smtpd_client_restrictions, $smtpd_helo_restrictions and $smtpd_sender_restrictions. Or, alternate route, wait until the ETRN command before evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions. patience is a virtue fr 💅
  • parent_domain_matches_subdomains (default: see postconf -d output) — a whole list of Postfix features where the pattern example.com also matches subdomains of example.com, instead of making you write out an explicit .example.com pattern. she's giving generous. 🫶
  • smtpd_client_restrictions (default: empty) — optional restrictions the Postfix SMTP server applies in the context of a client connection request.
  • smtpd_helo_required (default: no) — do you require that a remote SMTP client introduces itself with the HELO or EHLO command before sending MAIL or any other command that needs EHLO negotiation? your call bestie.
  • smtpd_helo_restrictions (default: empty) — optional restrictions the Postfix SMTP server applies in the context of a client HELO command.
  • smtpd_sender_restrictions (default: empty) — optional restrictions the Postfix SMTP server applies in the context of a client MAIL FROM command.
  • smtpd_recipient_restrictions (default: see postconf -d output) — optional restrictions the Postfix SMTP server applies in the context of a client RCPT TO command, and this happens after smtpd_relay_restrictions. order matters, ok? 👑
  • smtpd_etrn_restrictions (default: empty) — optional restrictions the Postfix SMTP server applies in the context of a client ETRN command.
  • allow_untrusted_routing (default: no) — forward mail with sender-specified routing, like user[@%!]remote[@%!]site, from untrusted clients to destinations that match $relay_domains. ngl this one is giving risky, tread carefully.
  • smtpd_restriction_classes (default: empty) — user-defined aliases for groups of access restrictions. nickname energy. 🎀
  • smtpd_null_access_lookup_key (default: <>) — the lookup key to be used in SMTP access(5) tables instead of the null sender address.
  • permit_mx_backup_networks (default: empty) — restrict the use of the permit_mx_backup SMTP access feature to only domains whose primary MX hosts match the listed networks.

🌸 Available in Postfix version 2.0 and later: 🌸

  • smtpd_data_restrictions (default: empty) — optional access restrictions that the Postfix SMTP server applies in the context of the SMTP DATA command.
  • smtpd_expansion_filter (default: see postconf -d output) — what characters are allowed in $name expansions of RBL reply templates.

🦋 Available in Postfix version 2.1 and later: 🦋

  • smtpd_reject_unlisted_sender (default: no) — request that the Postfix SMTP server rejects mail from unknown sender addresses, even when no explicit reject_unlisted_sender access restriction is specified.
  • smtpd_reject_unlisted_recipient (default: yes) — request that the Postfix SMTP server rejects mail for unknown recipient addresses, even when no explicit reject_unlisted_recipient access restriction is specified.

✨ Available in Postfix version 2.2 and later: ✨

  • smtpd_end_of_data_restrictions (default: empty) — optional access restrictions that the Postfix SMTP server applies in the context of the SMTP END-OF-DATA command.

💖 Available in Postfix version 2.10 and later: 💖

  • smtpd_relay_restrictions (default: permit_mynetworks, permit_sasl_authenticated, defer_unauth_destination) — access restrictions for mail relay control that the Postfix SMTP server applies in the context of the RCPT TO command, and this one runs before smtpd_recipient_restrictions. she goes first, periodt. 💅

🌈 SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS 🌈

ok so Postfix version 2.1 said "let there be verification" and thus sender and recipient address verification was born. ✨ the way this works is genuinely iconic: it's implemented by sending probe email messages that are not actually delivered. like, ghost emails. 👻 you ask for this feature via the reject_unverified_sender and reject_unverified_recipient access restrictions. the status of all those verification probes is maintained by the verify(8) server, and if you want the full tea on configuring and operating the Postfix sender/recipient address verification service, the file ADDRESS_VERIFICATION_README is right there waiting for you. 🫶

  • address_verify_poll_count (default: normal: 3, overload: 1) — how many times to query the verify(8) service for the completion of an address verification request that's still in progress.
  • address_verify_poll_delay (default: 3s) — the delay between queries for the completion of an address verification request that's still in progress.
  • address_verify_sender (default: $double_bounce_sender) — the sender address to use in address verification probes. heads up bestie: prior to Postfix 2.5 the default was "postmaster". glow-up era. 💅
  • unverified_sender_reject_code (default: 450) — the numerical Postfix SMTP server response code when a recipient address is rejected by the reject_unverified_sender restriction.
  • unverified_recipient_reject_code (default: 450) — the numerical Postfix SMTP server response when a recipient address is rejected by the reject_unverified_recipient restriction.

🎀 Available in Postfix version 2.6 and later: 🎀

  • unverified_sender_defer_code (default: 450) — the numerical Postfix SMTP server response code when a sender address probe fails due to a temporary error condition.
  • unverified_recipient_defer_code (default: 450) — the numerical Postfix SMTP server response when a recipient address probe fails due to a temporary error condition.
  • unverified_sender_reject_reason (default: empty) — the Postfix SMTP server's reply when rejecting mail with reject_unverified_sender.
  • unverified_recipient_reject_reason (default: empty) — the Postfix SMTP server's reply when rejecting mail with reject_unverified_recipient.
  • unverified_sender_tempfail_action (default: $reject_tempfail_action) — the Postfix SMTP server's action when reject_unverified_sender fails due to a temporary error condition.
  • unverified_recipient_tempfail_action (default: $reject_tempfail_action) — the Postfix SMTP server's action when reject_unverified_recipient fails due to a temporary error condition.

🦋 Available with Postfix 2.9 and later: 🦋

  • address_verify_sender_ttl (default: 0s) — the time between changes in the time-dependent portion of address verification probe sender addresses. she's time-sensitive fr. ⏰

💜 ACCESS CONTROL RESPONSES 💜

these next parameters control the numerical SMTP reply codes and/or the text responses. so like, what the server actually says back. 💅

  • access_map_reject_code (default: 554) — the numerical Postfix SMTP server response code for an access(5) map "reject" action.
  • defer_code (default: 450) — the numerical Postfix SMTP server response code when a remote SMTP client request is rejected by the "defer" restriction.
  • invalid_hostname_reject_code (default: 501) — the numerical Postfix SMTP server response code when the client HELO or EHLO command parameter is rejected by the reject_invalid_helo_hostname restriction.
  • maps_rbl_reject_code (default: 554) — the numerical Postfix SMTP server response code when a remote SMTP client request is blocked by the reject_rbl_client, reject_rhsbl_client, reject_rhsbl_reverse_client, reject_rhsbl_sender or reject_rhsbl_recipient restriction.
  • non_fqdn_reject_code (default: 504) — the numerical Postfix SMTP server reply code when a client request is rejected by the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender or reject_non_fqdn_recipient restriction.
  • plaintext_reject_code (default: 450) — the numerical Postfix SMTP server response code when a request is rejected by the reject_plaintext_session restriction.
  • reject_code (default: 554) — the numerical Postfix SMTP server response code when a remote SMTP client request is rejected by the "reject" restriction.
  • relay_domains_reject_code (default: 554) — the numerical Postfix SMTP server response code when a client request is rejected by the reject_unauth_destination recipient restriction.
  • unknown_address_reject_code (default: 450) — the numerical response code when the Postfix SMTP server rejects a sender or recipient address because its domain is unknown.
  • unknown_client_reject_code (default: 450) — the numerical Postfix SMTP server response code when a client without a valid address <=> name mapping is rejected by the reject_unknown_client_hostname restriction.
  • unknown_hostname_reject_code (default: 450) — the numerical Postfix SMTP server response code when the hostname specified with the HELO or EHLO command is rejected by the reject_unknown_helo_hostname restriction.

✨ Available in Postfix version 2.0 and later: ✨

  • default_rbl_reply (default: see postconf -d output) — the default Postfix SMTP server response template for a request that is rejected by an RBL-based restriction.
  • multi_recipient_bounce_reject_code (default: 550) — the numerical Postfix SMTP server response code when a remote SMTP client request is blocked by the reject_multi_recipient_bounce restriction.
  • rbl_reply_maps (default: empty) — optional lookup tables with RBL or RHSBL response templates.

🍓 Available in Postfix version 2.6 and later: 🍓

  • access_map_defer_code (default: 450) — the numerical Postfix SMTP server response code for an access(5) map "defer" action, including "defer_if_permit" or "defer_if_reject".
  • reject_tempfail_action (default: defer_if_permit) — the Postfix SMTP server's action when a reject-type restriction fails due to a temporary error condition.
  • unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action) — the Postfix SMTP server's action when reject_unknown_helo_hostname fails due to a temporary error condition.
  • unknown_address_tempfail_action (default: $reject_tempfail_action) — the Postfix SMTP server's action when reject_unknown_sender_domain or reject_unknown_recipient_domain fail due to a temporary error condition.

✨ MISCELLANEOUS CONTROLS ✨

okay bestie, this is the grab-bag section, the misc controls, the ones that don't fit anywhere else but absolutely run the whole vibe. let's get into it. 💅

  • config_directory — default is whatever postconf -d output says, bestie. it's the default location of the Postfix main.cf and master.cf configuration files. the config home base. 🏠
  • daemon_timeout (18000s) — how much time a Postfix daemon process may take to handle a request before it is terminated by a built-in watchdog timer. ⏰
  • command_directory — default is postconf -d output. the location of all postfix administrative commands. the command stash. 🛠️
  • double_bounce_sender (double-bounce) — the sender address of postmaster notifications that are generated by the mail system. double bounce, double drama? no, just the sender. 📬
  • ipc_timeout (3600s) — the time limit for sending or receiving information over an internal communication channel. ⏳
  • mail_name (Postfix) — the mail system name that is displayed in Received: headers, in the SMTP greeting banner, and in bounced mail. 🏷️
  • mail_owner (postfix) — the UNIX system account that owns the Postfix queue and most Postfix daemon processes. the boss account. 👑
  • max_idle (100s) — the maximum amount of time that an idle Postfix daemon process waits for an incoming connection before terminating voluntarily. it's giving "I'll wait, but not forever". 💤
  • max_use (100) — the maximal number of incoming connections that a Postfix daemon process will service before terminating voluntarily. 💯
  • myhostname — default is postconf -d output. the internet hostname of this mail system. 🖥️
  • mynetworks — default is postconf -d output. the list of "trusted" remote SMTP clients that have more privileges than "strangers". the VIP list. 🎟️
  • myorigin ($myhostname) — the domain name that locally-posted mail appears to come from, and that locally posted mail is delivered to. ✉️
  • process_id (read-only) — the process ID of a Postfix command or daemon process. read-only, so don't try to set it, just read it. 🔍
  • process_name (read-only) — the process name of a Postfix command or daemon process. read-only again. 📛
  • queue_directory — default is postconf -d output. the location of the Postfix top-level queue directory. the queue's main character location. 📂
  • recipient_delimiter (empty) — the set of characters that can separate an email address localpart, user name, or a .forward file name from its extension. default empty. 🔤
  • smtpd_banner ($myhostname ESMTP $mail_name) — the text that follows the 220 status code in the SMTP greeting banner. say hi with it. 👋
  • syslog_facility (mail) — the syslog facility of Postfix logging. 📝
  • syslog_name — default is postconf -d output. a prefix that is prepended to the process name in syslog records, so that, for example, "smtpd" becomes "prefix/smtpd". 🏷️

Available in Postfix version 2.2 and later:

  • smtpd_forbidden_commands (CONNECT GET POST regexp:{{/^[^A-Z]/ Bogus}}) — list of commands that cause the Postfix SMTP server to immediately terminate the session with a 221 code. 🚫

Available in Postfix version 2.5 and later:

  • smtpd_client_port_logging (no) — enable logging of the remote SMTP client port in addition to the hostname and IP address. 🔌

Available in Postfix 3.3 and later:

  • service_name (read-only) — the master.cf service name of a Postfix daemon process. read-only, bestie. 🧾

Available in Postfix 3.4 and later:

  • smtpd_reject_footer_maps (empty) — lookup tables, indexed by the complete Postfix SMTP server 4xx or 5xx response, with reject footer templates. 📇

Available in Postfix 3.10 and later:

  • smtpd_hide_client_session (no) — do not include SMTP client session information in the Postfix SMTP server's Received: message header. 🙈

👀 SEE ALSO 👀

📚 README FILES 📚

Use postconf readme_directory or postconf html_directory to locate this information. bestie, go ask Postfix where the docs live. 🔍

  • ADDRESS_CLASS_README — blocking unknown hosted or relay recipients
  • ADDRESS_REWRITING_README — Postfix address manipulation
  • BDAT_README — Postfix CHUNKING support
  • FILTER_README — external after-queue content filter
  • LOCAL_RECIPIENT_README — blocking unknown local recipients
  • MILTER_README — before-queue mail filter applications
  • SMTPD_ACCESS_README — built-in access policies
  • SMTPD_POLICY_README — external policy server
  • SMTPD_PROXY_README — external before-queue content filter
  • SASL_README — Postfix SASL howto
  • TLS_README — Postfix STARTTLS howto
  • VERP_README — Postfix XVERP extension
  • XCLIENT_README — Postfix XCLIENT extension
  • XFORWARD_README — Postfix XFORWARD extension

📜 LICENSE 📜

The Secure Mailer license must be distributed with this software.

no cap, that's the whole license line. keep it with the software, bestie. 💖

👑 AUTHOR(S) 👑

the icons who made this. 🫶

Wietse Venema IBM T.J. Watson Research P.O. Box 704 Yorktown Heights, NY 10598, USA

Wietse Venema Google, Inc. 111 8th Avenue New York, NY 10011, USA

Wietse Venema porcupine.org

SASL support originally by: Till Franke SuSE Rhein/Main AG 65760 Eschborn, Germany

TLS support originally by: Lutz Jaenicke BTU Cottbus Allgemeine Elektrotechnik Universitaetsplatz 3-4 D-03044 Cottbus, Germany

Revised TLS support by: Victor Duchovni Morgan Stanley

that's a wrap, bestie! the footer says SMTPD(8), and the source/version and date are chillin' right there in that footer like the little crown it is. so here's your cute sign-off: go forth, run your SMTP server, and stay iconic. 💖👑✨

📦 where this page comes from