SMTPD(8)

📦
version 3.11.7 · 9 versions
, in alpine 3.24, arch rolling, nixos 26.05, nixpkgs unstable, ubuntu stonking

💅 NAME 💅

okay bestie, welcome to smtpd(8) from the System Manager's Manual — the Postfix SMTP server, aka the main character of incoming mail. 💌

✨ SYNOPSIS ✨

smtpd [generic Postfix daemon options]

sendmail -bs

🦋 DESCRIPTION 🦋

The SMTP server accepts network connection requests and performs zero or more SMTP transactions per connection. No cap, it can do a whole little run of them. Each received message is piped through the cleanup(8) daemon, and is placed into 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.

Alternatively, the SMTP server can run in stand-alone mode; this is traditionally obtained 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. As of Postfix version 2.3, the SMTP server refuses to receive mail from the network when it runs with non $mail_owner privileges. 🫶

The SMTP server implements a variety of policies for connection requests, and for parameters given to HELO, ETRN, MAIL FROM, VRFY and RCPT TO commands. They are detailed below and in the main.cf configuration file.

🔐 SECURITY 🔐

The SMTP server is moderately security-sensitive. It talks to SMTP clients and to DNS servers on the network. The SMTP server can be run chrooted at fixed low privilege. Lowkey important, so don't sleep on it.

📜 STANDARDS 📜

the vibe check says this server plays by these rules, and we are not skipping any of them:

🩺 DIAGNOSTICS 🩺

Problems and transactions are logged to syslogd(8) or postlogd(8).

Depending on the setting of the notify_classes parameter, the postmaster is notified of bounces, protocol problems, policy violations, and of other trouble. So yeah, the postmaster gets the updates. 💀

⚙️ CONFIGURATION PARAMETERS ⚙️

Changes to main.cf are picked up automatically, as 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. It's giving "summary now, deep lore later." ✨

🧩 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. Basically: other software did what now? 🙈

  • 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 the lore drop for address glow-ups.

  • 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. It's giving "mail goes out, mail comes back, everyone eats." 🔥

  • 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. ⏳

💌 BEFORE QUEUE MILTER CONTROLS 💌

Okay so bestie, as of version 2.3, Postfix supports the Sendmail version 8 Milter (mail filter) protocol. These content filters run outside Postfix. They can inspect the SMTP command stream and the message content, and they can request modifications before mail is queued. For the full tea, see the MILTER_README document. 🫶✨

  • smtpd_milters (empty) — A list of Milter (mail filter) applications for new mail that arrives via the Postfix smtpd(8) server. 💌
  • milter_protocol (6) — The mail filter protocol version, plus any optional protocol extensions, for communication with a Milter application; prior to Postfix 2.6 the default protocol is 2. 📨
  • milter_default_action (Postfix >= 3.11: shutdown; Postfix < 3.11: tempfail) — The default action when a Milter (mail filter) response is unavailable (for example, bad Postfix configuration or Milter failure). 🚨
  • 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 are sent to Milter (mail filter) applications after completion of an SMTP connection. 🔌
  • milter_helo_macros (see 'postconf -d' output) — The macros that are sent to Milter (mail filter) applications after the SMTP HELO or EHLO command. 👋
  • milter_mail_macros (see 'postconf -d' output) — The macros that are sent to Milter (mail filter) applications after the SMTP MAIL FROM command. 📤
  • milter_rcpt_macros (see 'postconf -d' output) — The macros that are sent to Milter (mail filter) applications after the SMTP RCPT TO command. 📥
  • milter_data_macros (see 'postconf -d' output) — The macros that are 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 are 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 are sent to Milter (mail filter) applications after the end of the message header. 📝
  • milter_end_of_data_macros (see 'postconf -d' output) — The macros that are 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 specify default values for arbitrary macros that Postfix may send to Milter applications. 🎀

🌈 Available in Postfix version 3.2 and later 🌈

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

🔍 GENERAL CONTENT INSPECTION CONTROLS 🔍

The following parameters are applicable for both built-in and external content filters. 💅

⭐ Available in Postfix version 2.1 and later ⭐

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

🛰️ EXTERNAL CONTENT INSPECTION CONTROLS 🛰️

The following parameters are applicable for both before-queue and after-queue content filtering. 🧚

🌸 Available in Postfix version 2.1 and later 🌸

  • smtpd_authorized_xforward_hosts (empty) — What remote SMTP clients are allowed 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) — Enable 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 list of available features depends on the SASL server implementation that is selected 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) — What 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 information that the Postfix SMTP server passes through to the SASL plug-in implementation that is selected 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 that is passed to the SASL plug-in that is 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. 🎯

✨ TLS SUPPORT CONTROLS ✨

okay bestie, if you want the full deep-dive on STARTTLS config, the TLS_README document has you covered — that's the main character of TLS docs, go read it 💅

  • 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 the ancient smtpd_use_tls and smtpd_enforce_tls parameters. out with the old, in with the new 🦋
  • smtpd_sasl_tls_security_options ($smtpd_sasl_security_options) — the SASL auth security options the Postfix SMTP server uses for TLS-encrypted SMTP sessions. encrypted slay only ✨
  • smtpd_starttls_timeout (see postconf -d output) — the time limit for Postfix SMTP server write and read operations while the TLS startup and shutdown handshakes are doing their thing. don't ghost the handshake fr ⏳
  • smtpd_tls_CAfile (empty) — a file holding (PEM format) CA certificates of root CAs that are trusted to sign either remote SMTP client certificates or intermediate CA certificates 🔐
  • smtpd_tls_CApath (empty) — a directory holding (PEM format) CA certificates of root CAs trusted to sign either remote SMTP client certificates or intermediate CA certificates. same vibe as CAfile, just directory-flavoured 🎀
  • smtpd_tls_always_issue_session_ids (yes) — forces the Postfix SMTP server to issue a TLS session id, even when TLS session caching is turned off (that's when smtpd_tls_session_cache_database is empty) 👑
  • smtpd_tls_ask_ccert (no) — ask a remote SMTP client for a client certificate. polite queen behaviour 🫶
  • smtpd_tls_auth_only (no) — when TLS encryption is optional on the Postfix SMTP server, don't announce or accept SASL authentication over unencrypted connections. no plaintext passwords, periodt 💀
  • smtpd_tls_ccert_verifydepth (9) — the verification depth for remote SMTP client certificates 🧐
  • smtpd_tls_cert_file (empty) — file with the Postfix SMTP server RSA certificate in PEM format 📜
  • smtpd_tls_exclude_ciphers (empty) — list of ciphers or cipher types to exclude from the SMTP server cipher list at all TLS security levels 🙅‍♀️
  • smtpd_tls_dcert_file (empty) — file with the Postfix SMTP server DSA certificate in PEM format
  • smtpd_tls_dh1024_param_file (empty) — file with DH parameters the Postfix SMTP server should use with non-export EDH ciphers 🌸
  • smtpd_tls_dh512_param_file (empty) — file with DH parameters the Postfix SMTP server should use with export-grade EDH ciphers
  • smtpd_tls_dkey_file ($smtpd_tls_dcert_file) — file with the Postfix SMTP server DSA private key in PEM format. keep it secret, keep it safe 🔑
  • smtpd_tls_key_file ($smtpd_tls_cert_file) — file with the Postfix SMTP server RSA private key in PEM format
  • smtpd_tls_loglevel (0) — enables extra Postfix SMTP server logging of TLS activity. turn it up if you're debugging, bestie 🔍
  • smtpd_tls_mandatory_ciphers (medium) — the minimum TLS cipher grade the Postfix SMTP server will use with mandatory TLS encryption
  • smtpd_tls_mandatory_exclude_ciphers (empty) — an additional list of ciphers or cipher types to exclude from the Postfix SMTP server cipher list at mandatory TLS security levels
  • smtpd_tls_mandatory_protocols (see postconf -d output) — the TLS protocols accepted by the Postfix SMTP server with mandatory TLS encryption
  • smtpd_tls_received_header (no) — asks the Postfix SMTP server to produce Received: message headers that include info about the protocol and cipher used, plus the remote SMTP client CommonName and the client certificate issuer CommonName 🏷️
  • smtpd_tls_req_ccert (no) — with mandatory TLS encryption, require a trusted remote SMTP client certificate before allowing TLS connections to proceed. no cert, no entry 🚪
  • smtpd_tls_wrappermode (no) — run the Postfix SMTP server in TLS "wrapper" mode instead of using the STARTTLS command 🎁
  • 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 to seed its internal pseudo random number generator (PRNG) 🎲
  • tls_high_cipherlist (see postconf -d output) — the OpenSSL cipherlist for "high" grade ciphers
  • tls_medium_cipherlist (see postconf -d output) — the OpenSSL cipherlist for "medium" or higher grade ciphers
  • tls_null_cipherlist (eNULL:!aNULL) — the OpenSSL cipherlist for "NULL" grade ciphers that provide authentication without encryption 👀

Available in Postfix version 2.3..3.7:

  • tls_low_cipherlist (see postconf -d output) — the OpenSSL cipherlist for "low" or higher grade ciphers
  • tls_export_cipherlist (see postconf -d output) — the OpenSSL cipherlist for "export" or higher grade ciphers

Available in Postfix version 2.5 and later:

  • smtpd_tls_fingerprint_digest (see postconf -d output) — the message digest algorithm used to construct remote SMTP client-certificate fingerprints, or public key fingerprints (Postfix 2.9 and later), for check_ccert_access and permit_tls_clientcerts 🫆

Available in Postfix version 2.6 and later:

  • smtpd_tls_protocols (see postconf -d output) — the TLS protocols accepted by the Postfix SMTP server with opportunistic TLS encryption
  • smtpd_tls_ciphers (medium) — the minimum TLS cipher grade the Postfix SMTP server will use with opportunistic TLS encryption
  • smtpd_tls_eccert_file (empty) — file with the Postfix SMTP server ECDSA certificate in PEM format 🌿
  • smtpd_tls_eckey_file ($smtpd_tls_eccert_file) — file with the Postfix SMTP server ECDSA private key in PEM format
  • smtpd_tls_eecdh_grade (see postconf -d output) — the Postfix SMTP server security grade for ephemeral elliptic-curve Diffie-Hellman (EECDH) key exchange
  • tls_eecdh_strong_curve (prime256v1) — the elliptic curve the Postfix SMTP server uses for sensibly strong ephemeral ECDH key exchange 💪
  • tls_eecdh_ultra_curve (secp384r1) — the elliptic curve the Postfix SMTP server uses for maximally strong ephemeral ECDH key exchange. ultra, as the name literally says 🔥

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. my list, my rules 👑
  • tls_disable_workarounds (see postconf -d output) — list or bit-mask of OpenSSL bug work-arounds to disable 🐛

Available in Postfix version 2.11 and later:

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

Available in Postfix version 3.0 and later:

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

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

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 ⛓️
  • 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 🗺️

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 it's shutting down a TLS session, until Postfix times out 😭 nobody likes a hang

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

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
  • tls_config_name (empty) — the application name Postfix passes to OpenSSL library initialization functions

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 🔑

Available in Postfix version 3.11 and later:

  • requiretls_enable (yes) — enable support for the ESMTP verb REQUIRETLS in the MAIL FROM command ✉️
  • requiretls_esmtp_header (yes) — record the ESMTP REQUIRETLS request in a Require-TLS-ESMTP: yes message header

🫠 OBSOLETE TLS CONTROLS 🫠

okay these ones are giving vintage, and not in a cute thrifted way — they only exist for compatibility with Postfix versions before 2.3, and support for them will be removed in a future release. so like, don't build your whole personality on them bestie 😭

  • smtpd_use_tls (no) — opportunistic TLS: announce STARTTLS support to remote SMTP clients, but don't require that clients use TLS encryption
  • 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. everybody else, blocked 💅
  • smtpd_tls_cipherlist (empty) — obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher list 🦕

🌈 SMTPUTF8 CONTROLS 🌈

preliminary SMTPUTF8 support showed up in Postfix 3.0 — it's giving early-access era, but it's here ✨

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

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's used for DNS lookups 🦋

💌 VERP SUPPORT CONTROLS 💌

Okay so bestie, VERP style delivery is a whole vibe: each recipient of a message receives a customized copy of the message with his/her own recipient address encoded in the envelope sender address. The VERP_README file describes configuration and operation details of Postfix support for variable envelope return path addresses. VERP style delivery is requested with the SMTP XVERP command or with the sendmail -V command-line option and is available in Postfix version 1.1 and later. ✨

  • default_verp_delimiters (+=) — the two default VERP delimiter characters. 💅
  • 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.

🛠️ 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. Like, pick your debugging era, honestly. 🔍

  • 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.
  • 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. 🛟

✨ 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).

👯 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 information on this topic is in the LOCAL_RECIPIENT_README and ADDRESS_CLASS_README documents. 🫶

  • 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.
  • 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 section is literally about keeping your server from getting absolutely steamrolled. 💖 The following parameters limit resource usage by the SMTP server and/or control client request rates.

  • line_length_limit (2048) — upon input, long lines are chopped up into pieces of at most this length; upon delivery, long lines are reconstructed. ✂️
  • queue_minfree (0) — the minimal amount of free space in bytes in the queue file system that is needed to receive mail. yes, bytes, not vibes.
  • message_size_limit (10240000) — the maximal size in bytes of a message, including envelope information. the whole package. 🎁
  • smtpd_recipient_limit (1000) — the maximal number of recipients that the Postfix SMTP server accepts per message delivery request. 👯
  • smtpd_timeout (normal: 300s, overload: 10s) — when the Postfix SMTP server wants to send an SMTP server response, how long it will wait for an underlying network write operation to complete; and when the Postfix SMTP server wants to receive an SMTP client request, how long it will wait for an underlying network read operation to complete. ⏳
  • smtpd_history_flush_threshold (100) — the maximal number of lines in the Postfix SMTP server command history before it is flushed upon receipt of EHLO, RSET, or end of DATA. 🧹

Available in Postfix version 2.3 and later: ✨

  • smtpd_peername_lookup (yes) — attempt to look up the remote SMTP client hostname, and verify that the name matches the client IP address. 🔍

The per SMTP client connection count and request rate limits are implemented in co-operation with the anvil(8) service, and are available in Postfix version 2.2 and later. 🛰️

  • smtpd_client_connection_count_limit (50) — how many simultaneous connections any client is allowed to make to this service. 🚦
  • smtpd_client_connection_rate_limit (0) — the maximal number of connection attempts any client is allowed to make to this service per time unit. ⏱️
  • smtpd_client_message_rate_limit (0) — the maximal number of message delivery requests that any client is allowed to make to this service per time unit, regardless of whether or not Postfix actually accepts those messages. 📨
  • smtpd_client_recipient_rate_limit (0) — the maximal number of recipient addresses that any client is allowed to send to this service per time unit, regardless of whether or not Postfix actually accepts those recipients. 📮
  • smtpd_client_event_limit_exceptions ($mynetworks) — clients that are excluded from smtpd_client_*_count/rate_limit restrictions. 🫶

Available in Postfix version 2.3 and later: ✨

  • smtpd_client_new_tls_session_rate_limit (0) — the maximal number of new (i.e., uncached) TLS sessions that a remote SMTP client is allowed to negotiate with this service per time unit. 🔐

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 3.1 and later: 🔑

  • smtpd_client_auth_rate_limit (0) — the maximal number of AUTH commands that any client is allowed to send to this service per time unit, regardless of whether or not Postfix actually accepts those commands.

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. 💨
  • header_from_format (standard) — the format of the Postfix-generated From: header. 💌

Available in Postfix version 3.8 and later: 🧮

  • smtpd_client_ipv4_prefix_length (32) — aggregate smtpd_client_*_count and smtpd_client_*_rate statistics by IPv4 network blocks with the specified network prefix.
  • smtpd_client_ipv6_prefix_length (84) — aggregate smtpd_client_*_count and smtpd_client_*_rate statistics by IPv6 network blocks with the specified network prefix.

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

  • smtpd_forbid_unauth_pipelining (Postfix >= 3.9: yes) — disconnect remote SMTP clients that violate RFC 2920 (or 5321) command pipelining constraints.

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

  • smtpd_forbid_bare_newline (Postfix >= 3.9: normalize) — reject or restrict input lines from an SMTP client that end in <LF> instead of the standard <CR><LF>.
  • smtpd_forbid_bare_newline_exclusions ($mynetworks) — exclude the specified clients from smtpd_forbid_bare_newline enforcement. 🙈

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

🔥 TARPIT CONTROLS 🔥

When a remote SMTP client makes errors, the Postfix SMTP server can insert delays before responding. this can help to slow down run-away software. 🐢 The behavior is controlled 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 (1s) — with Postfix version 2.1 and later: the SMTP server response delay 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 (10) — the number of errors a remote SMTP client is allowed to make without delivering mail before the Postfix SMTP server slows down all its responses. 🐌
  • smtpd_hard_error_limit (normal: 20, overload: 1) — the maximal number of errors a remote SMTP client is allowed to make without delivering mail. 🛑
  • smtpd_junk_command_limit (normal: 100, overload: 1) — the number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote SMTP client can send before the Postfix SMTP server starts to increment the error counter with each junk command. 🗑️

Available in Postfix version 2.1 and later: ✨

  • smtpd_recipient_overshoot_limit (1000) — the number of recipients that a remote SMTP client can send in excess of the limit specified 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 that runs outside Postfix. See the file SMTPD_POLICY_README for more information. 📜

  • smtpd_policy_service_max_idle (300s) — the time after which an idle SMTPD policy service connection is closed. 😴
  • smtpd_policy_service_max_ttl (1000s) — the time after which an active SMTPD policy service connection is closed. ⏲️
  • smtpd_policy_service_timeout (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 (451 4.3.5 Server configuration problem) — the default action when an SMTPD policy service request fails.
  • smtpd_policy_service_request_limit (0) — the maximal number of requests per SMTPD policy service connection, or zero (no limit). 0️⃣
  • smtpd_policy_service_try_limit (2) — the maximal number of attempts to send an SMTPD policy service request before giving up. 🔁
  • smtpd_policy_service_retry_delay (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 (empty) — optional information that the Postfix SMTP server specifies in the "policy_context" attribute of a policy service request (originally, to share the same service endpoint among multiple check_policy_service clients). ✨

🔐 ACCESS CONTROLS 🔐

ok so before we even get into the params, bestie, there's a whole doc for this: the SMTPD_ACCESS_README document gives an introduction to all the SMTP server access control features. like, that's the lore. go read it 💅

  • smtpd_delay_reject (yes) — this one's the procrastinator of the group and honestly same. It waits until the RCPT TO command before evaluating $smtpd_client_restrictions, $smtpd_helo_restrictions and $smtpd_sender_restrictions, or it waits until the ETRN command before evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions. no cap, it's just delaying the vibe check ✨
  • parent_domain_matches_subdomains (see postconf -d output) — a list of Postfix features where the pattern "example.com" also matches subdomains of example.com, instead of requiring an explicit ".example.com" pattern. yes, it's nepo-baby matching 🎀
  • smtpd_client_restrictions (empty) — optional restrictions that the Postfix SMTP server applies in the context of a client connection request.
  • smtpd_helo_required (no) — require that a remote SMTP client introduces itself with the HELO or EHLO command before sending the MAIL command or other commands that require EHLO negotiation. like, say hi first?? basic manners 💅
  • smtpd_helo_restrictions (empty) — optional restrictions that the Postfix SMTP server applies in the context of a client HELO command.
  • smtpd_sender_restrictions (empty) — optional restrictions that the Postfix SMTP server applies in the context of a client MAIL FROM command.
  • smtpd_recipient_restrictions (see postconf -d output) — optional restrictions that the Postfix SMTP server applies in the context of a client RCPT TO command, after smtpd_relay_restrictions. yes, after. order matters, icon behavior 👑
  • smtpd_etrn_restrictions (empty) — optional restrictions that the Postfix SMTP server applies in the context of a client ETRN command.
  • allow_untrusted_routing (no) — forward mail with sender-specified routing (user[@%!]remote[@%!]site) from untrusted clients to destinations matching $relay_domains. that bracket situation is giving chaos but ok 😭
  • smtpd_restriction_classes (empty) — user-defined aliases for groups of access restrictions. it's giving nicknames for your friend group 🫶
  • smtpd_null_access_lookup_key (<>) — the lookup key to be used in SMTP access(5) tables instead of the null sender address.
  • permit_mx_backup_networks (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 (empty) — optional access restrictions that the Postfix SMTP server applies in the context of the SMTP DATA command.
  • smtpd_expansion_filter (see postconf -d output) — what characters are allowed in $name expansions of RBL reply templates. gatekeeping, but make it regex-adjacent 🌸

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. it said "who even are you" 💀
  • smtpd_reject_unlisted_recipient (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 (empty) — optional access restrictions that the Postfix SMTP server applies in the context of the SMTP END-OF-DATA command. the finale has rules too ✨

Available in Postfix version 2.10 and later:

  • smtpd_relay_restrictions (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, before smtpd_recipient_restrictions. before bestie, before. the sequencing is the whole plot 🔥

🕵️ SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS 🕵️

Postfix version 2.1 introduces sender and recipient address verification. This feature is implemented by sending probe email messages that are not actually delivered — yes, ghost messages, they're literally just out here collecting intel 👻. This feature is requested via the reject_unverified_sender and reject_unverified_recipient access restrictions. The status of verification probes is maintained by the verify(8) server. See the file ADDRESS_VERIFICATION_README for information about how to configure and operate the Postfix sender/recipient address verification service. that's the manual's manual, iykyk 📖

  • address_verify_poll_count (normal: 3, overload: 1) — how many times to query the verify(8) service for the completion of an address verification request in progress. yes she's checking her phone that many times 📱
  • address_verify_poll_delay (3s) — the delay between queries for the completion of an address verification request in progress.
  • address_verify_sender ($double_bounce_sender) — the sender address to use in address verification probes; prior to Postfix 2.5 the default was "postmaster". glow-up documented ✅
  • unverified_sender_reject_code (450) — the numerical Postfix SMTP server response code when a recipient address is rejected by the reject_unverified_sender restriction.
  • unverified_recipient_reject_code (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 (450) — the numerical Postfix SMTP server response code when a sender address probe fails due to a temporary error condition.
  • unverified_recipient_defer_code (450) — the numerical Postfix SMTP server response when a recipient address probe fails due to a temporary error condition.
  • unverified_sender_reject_reason (empty) — the Postfix SMTP server's reply when rejecting mail with reject_unverified_sender. it's giving custom rejection text, be creative 🎀
  • unverified_recipient_reject_reason (empty) — the Postfix SMTP server's reply when rejecting mail with reject_unverified_recipient.
  • unverified_sender_tempfail_action ($reject_tempfail_action) — the Postfix SMTP server's action when reject_unverified_sender fails due to a temporary error condition.
  • unverified_recipient_tempfail_action ($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 (0s) — the time between changes in the time-dependent portion of address verification probe sender addresses. rotating the alias, iconic ⭐

📢 ACCESS CONTROL RESPONSES 📢

The following parameters control numerical SMTP reply codes and/or text responses. basically the whole "what do we say back" situation 💬

  • access_map_reject_code (554) — the numerical Postfix SMTP server response code for an access(5) map "reject" action.
  • defer_code (450) — the numerical Postfix SMTP server response code when a remote SMTP client request is rejected by the "defer" restriction.
  • invalid_hostname_reject_code (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 (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. that's a whole squad of RBLs ngl 😭
  • non_fqdn_reject_code (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 (450) — the numerical Postfix SMTP server response code when a request is rejected by the reject_plaintext_session restriction.
  • reject_code (554) — the numerical Postfix SMTP server response code when a remote SMTP client request is rejected by the "reject" restriction.
  • relay_domains_reject_code (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 (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 (450) — the numerical Postfix SMTP server response code when a client without valid address <=> name mapping is rejected by the reject_unknown_client_hostname restriction.
  • unknown_hostname_reject_code (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 (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 (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 (empty) — optional lookup tables with RBL or RHSBL response templates.

Available in Postfix version 2.6 and later:

  • access_map_defer_code (450) — the numerical Postfix SMTP server response code for an access(5) map "defer" action, including "defer_if_permit" or "defer_if_reject". the if-statements of deferral, we love a conditional queen 💅
  • reject_tempfail_action (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 ($reject_tempfail_action) — the Postfix SMTP server's action when reject_unknown_helo_hostname fails due to a temporary error condition.
  • unknown_address_tempfail_action ($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.
ngl bestie, all these codes are just the server picking a personality for each rejection. 4xx = "try again later babe", 5xx = "no ❤️". memorize the vibe and you're golden 🫶

🎀 MISCELLANEOUS CONTROLS 🎀

Okay bestie, this is the grab-bag section — all the little knobs that don't fit anywhere else but absolutely still matter 💅

  • config_directory (default: see postconf -d output) — where the Postfix main.cf and master.cf config files live by default. That's the home base, the main character address of your setup 🏠
  • daemon_timeout (default 18000s) — how long a Postfix daemon process is allowed to keep grinding on one request before a built-in watchdog timer just mercs it 😭
  • command_directory (default: see postconf -d output) — the spot where all the postfix administrative commands hang out.
  • double_bounce_sender (default double-bounce) — the sender address used for postmaster notifications that the mail system itself generates. yes, the bounce of a bounce has an address. iconic honestly 🎾
  • ipc_timeout (default 3600s) — the time limit for sending or receiving info over an internal communication channel.
  • mail_name (default Postfix) — the mail system name that shows up in Received: headers, in the SMTP greeting banner, and in bounced mail. it's giving name tag energy 🏷️
  • mail_owner (default postfix) — the UNIX system account that owns the Postfix queue and most Postfix daemon processes.
  • max_idle (default 100s) — the max amount of time an idle Postfix daemon process waits for an incoming connection before it terminates voluntarily. it's not ghosting you, it's just on a schedule 💀
  • max_use (default 100) — the maximal number of incoming connections a Postfix daemon process will service before terminating voluntarily.
  • myhostname (default: see postconf -d output) — the internet hostname of this mail system.
  • mynetworks (default: see postconf -d output) — the list of "trusted" remote SMTP clients that get more privileges than "strangers". vip list behavior, no cap 👑
  • myorigin (default $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.
  • process_name (read-only) — the process name of a Postfix command or daemon process.
  • queue_directory (default: see postconf -d output) — the location of the Postfix top-level queue directory.
  • recipient_delimiter (default: empty) — the set of characters that can separate an email address localpart, user name, or a .forward file name from its extension.
  • smtpd_banner (default $myhostname ESMTP $mail_name) — the text that follows the 220 status code in the SMTP greeting banner. it's literally the first thing anyone hears from your server, so make it cute ✨
  • syslog_facility (default mail) — the syslog facility of Postfix logging.
  • syslog_name (default: see postconf -d output) — a prefix that gets 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 (default 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. the ban list, fr fr 🚫

🦋 Available in Postfix version 2.5 and later 🦋

  • smtpd_client_port_logging (default no) — enable logging of the remote SMTP client port in addition to the hostname and IP address. more receipts in the logs 🔍

💜 Available in Postfix 3.3 and later 💜

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

🍓 Available in Postfix 3.4 and later 🍓

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

🌈 Available in Postfix version 3.11 and later 🌈

  • smtpd_reject_filter_maps (default: empty) — an optional filter that can replace a reject response from the Postfix SMTP server itself, or from a program that replies through the Postfix SMTP server.

👀 SEE ALSO 👀

📚 README FILES 📚

Use postconf readme_directory or postconf html_directory to locate this information. like, the directions are literally in the config, bestie 🗺️

  • 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. yes, legally required, not optional 💅

🫶 AUTHOR(S) 🫶

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

and that's a wrap on the whole SMTPD(8) page, bestie 🎉 you read all of it, genuinely iconic behavior 👑 the footer down there just says SMTPD(8) so you know exactly which page you've been living in this whole time. go forth and slay your mail server configs 💖✨🎀

📦 where this page comes from