SMTPD(8postfix)

📦
version 3.8.6 · 4 versions
, in ubuntu noble

💌 SMTPD — the Postfix SMTP server, bestie edition

okay so this is smtpd(8postfix), aka the Postfix SMTP server. it's the part of Postfix that actually talks to other mail servers and goes "hi yes hello, what can i get you 🫶". buckle up, she's a long one.

✨ NAME ✨

smtpd — Postfix SMTP server 💅

✨ SYNOPSIS ✨

smtpd [generic Postfix daemon options]

sendmail -bs

✨ DESCRIPTION ✨

so basically? the SMTP server takes network connection requests and then does zero or more SMTP transactions on each connection (yes, zero — she can just vibe and leave, that's valid). every message she receives gets piped through the cleanup(8) daemon and dropped 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, no cap.

alternatively, the SMTP server can run in stand-alone mode — that's traditionally what you get with "sendmail -bs". and here's the tea 🍵: 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. but — as of Postfix version 2.3, the SMTP server refuses to receive mail from the network when it runs with non $mail_owner privileges. periodt.

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

🔒 SECURITY 🔒

the SMTP server is moderately security-sensitive — not the drama queen of the daemons, but she's out here. she talks to SMTP clients and to DNS servers on the network. the SMTP server can be run chrooted at fixed low privilege, which is a nice lil safety blanket 🧚

📜 STANDARDS 📜

she's certified, she's read the whole syllabus, she cites her sources:

🩺 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. like, she will tell on you, but affectionately 💖

⚙️ CONFIGURATION PARAMETERS ⚙️

changes to main.cf are picked up automatically, because smtpd(8) processes only run for a limited amount of time — she's not clingy, she moves on. if you want the change to happen faster, run "postfix reload". slay.

the text below provides only a parameter summary. see postconf(5) for more details including examples (aka the director's commentary).

🛠️ COMPATIBILITY CONTROLS 🛠️

these parameters work around implementation errors in other software, and/or let you override standards in order to prevent undesirable use. translation: sometimes other people's code is doing the most, and these are the workarounds 💀

  • broken_sasl_auth_clients (default: no) — enable interoperability with remote SMTP clients that implement an obsolete version of the AUTH command (RFC 4954).
  • disable_vrfy_command (default: no) — disable the SMTP VRFY command.
  • smtpd_noop_commands (default: 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 (default: 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 (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_sasl_exceptions_networks (default: 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 (default: 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 (default: 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 (default: 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 (default: 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 (default: 0) — an optional workaround for routers that break TCP window scaling.

Available in Postfix version 2.7 and later:

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

Available in Postfix version 2.9 - 3.6:

  • smtpd_per_record_deadline (default: 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 (default: empty) — optional filter for Postfix SMTP server DNS lookup results.

Available in Postfix 3.5 and later:

  • info_log_address_format (default: 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 (default: see 'postconf -d' output) — evaluate smtpd_relay_restrictions before smtpd_recipient_restrictions.
  • known_tcp_ports (default: 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 (default: 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 (default: 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 ✨lore✨.

  • receive_override_options (default: 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 (default: 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 (default: empty) — the name of the proxy protocol used by an optional before-smtpd proxy agent.
  • smtpd_upstream_proxy_timeout (default: 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 (default: 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 (default: empty) — the hostname and TCP port of the mail filtering proxy server.
  • smtpd_proxy_ehlo (default: $myhostname) — how the Postfix SMTP server announces itself to the proxy filter.
  • smtpd_proxy_options (default: empty) — list of options that control how the Postfix SMTP server communicates with a before-queue content filter.
  • smtpd_proxy_timeout (default: 100s) — the time limit for connecting to a proxy filter and for sending or receiving information.

okay bestie there's SO much more where that came from, stay tuned 🌈

🎀 BEFORE QUEUE MILTER CONTROLS 🎀

okay so as of version 2.3, Postfix is out here supporting the Sendmail version 8 Milter (mail filter) protocol, and honestly? iconic. These content filters live outside Postfix (they're the cool kids in their own house 💅). They can peek at the SMTP command stream and the message content, and they can ask for modifications before mail gets queued. For the whole lore, go read the MILTER_README document. 🦋

  • smtpd_milters (empty) — the list of Milter (mail filter) applications that get to handle new mail arriving through the Postfix smtpd(8) server.
  • milter_protocol (6) — the mail filter protocol version, plus any optional protocol extensions, used for talking to a Milter application. Heads up bestie: before Postfix 2.6 the default protocol is 2. 💀
  • milter_default_action (tempfail) — the default action to take when a Milter (mail filter) response just... isn't available (like, bad Postfix config or the Milter flat-out failed, rip).
  • 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 completed.
  • 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 end of the message header.
  • 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) — an optional list of name=value pairs that specify default values for arbitrary macros that Postfix may send to Milter applications. cute little safety net fr fr 💖

✨ Available in Postfix version 3.2 and later ✨

  • smtpd_milter_maps (empty) — lookup tables with Milter settings per remote SMTP client IP address. slay, per-client vibes 👑

🌈 GENERAL CONTENT INSPECTION CONTROLS 🌈

The following parameters are applicable for both built-in and external content filters. equal opportunity inspecting, we love to see it.

✨ Available in Postfix version 2.1 and later ✨

  • receive_override_options (empty) — enable or disable recipient validation, built-in content filtering, or address mapping. the lil on/off switch for the whole vibe check 🔥

🦋 EXTERNAL CONTENT INSPECTION CONTROLS 🦋

The following parameters are applicable for both before-queue and after-queue content filtering. both timelines, same rules.

✨ Available in Postfix version 2.1 and later ✨

  • smtpd_authorized_xforward_hosts (empty) — which remote SMTP clients are allowed to use the XFORWARD feature. gatekeeping, but make it deliberate ✨

💜 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. Two-way authentication?? we love a mutual moment 🫶. See the SASL_README document for the details.

  • broken_sasl_auth_clients (no) — enable interoperability with remote SMTP clients that implement an obsolete version of the AUTH command (RFC 4954). yes we're being nice to the old ones 💀
  • 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. and bestie, as of Postfix 2.3 the list of available features depends on the SASL server implementation that's selected with smtpd_sasl_type. so like, pick your fighter first 🎀
  • smtpd_sender_login_maps (empty) — optional lookup table with the SASL login names that own the sender (MAIL FROM) addresses. mapping who's allowed to send as who, no cap.

✨ 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. the "you don't get the invite" list 🙈

✨ 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's 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. just the one job but she does it 💅

✨ Available in Postfix version 2.11 and later ✨

  • smtpd_sasl_service (smtp) — the service name that gets 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. know your limits bestie 🌸

✨ 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. curating the lineup, periodt 👑

✨ STARTTLS SUPPORT CONTROLS ✨

okay bestie, if you want the full deep-dive on how to set up STARTTLS, the TLS_README document has all the tea ☕💖.

  • smtpd_tls_security_level (empty) — The SMTP TLS security level for the Postfix SMTP server; when you set a non-empty value, it overrides the obsolete smtpd_use_tls and smtpd_enforce_tls parameters. no cap.
  • smtpd_sasl_tls_security_options ($smtpd_sasl_security_options) — The SASL authentication security options that the Postfix SMTP server uses for TLS encrypted SMTP sessions. 🔐
  • smtpd_starttls_timeout (see 'postconf -d' output) — The time limit for Postfix SMTP server write and read operations during TLS startup and shutdown handshake procedures. ⏳
  • smtpd_tls_CAfile (empty) — A file containing (PEM format) CA certificates of root CAs trusted to sign either remote SMTP client certificates or intermediate CA certificates.
  • smtpd_tls_CApath (empty) — A directory containing (PEM format) CA certificates of root CAs trusted to sign either remote SMTP client certificates or intermediate CA certificates.
  • smtpd_tls_always_issue_session_ids (yes) — Force the Postfix SMTP server to issue a TLS session id, even when TLS session caching is turned off (smtpd_tls_session_cache_database is empty). 💅
  • smtpd_tls_ask_ccert (no) — Ask a remote SMTP client for a client certificate.
  • smtpd_tls_auth_only (no) — When TLS encryption is optional in the Postfix SMTP server, do not announce or accept SASL authentication over unencrypted connections. periodt. 🚫
  • smtpd_tls_ccert_verifydepth (9) — The verification depth for remote SMTP client certificates.
  • smtpd_tls_cert_file (empty) — File with the Postfix SMTP server RSA certificate in PEM format. 🎀
  • smtpd_tls_exclude_ciphers (empty) — List of ciphers or cipher types to exclude from the SMTP server cipher list at all TLS security levels.
  • smtpd_tls_dcert_file (empty) — File with the Postfix SMTP server DSA certificate in PEM format.
  • smtpd_tls_dh1024_param_file (empty) — File with DH parameters that the Postfix SMTP server should use with non-export EDH ciphers.
  • smtpd_tls_dh512_param_file (empty) — File with DH parameters that the Postfix SMTP server should use with export-grade EDH ciphers.
  • smtpd_tls_dkey_file ($smtpd_tls_dcert_file) — File with the Postfix SMTP server DSA private key in PEM format. 🔑
  • smtpd_tls_key_file ($smtpd_tls_cert_file) — File with the Postfix SMTP server RSA private key in PEM format. 🔑
  • smtpd_tls_loglevel (0) — Enable additional Postfix SMTP server logging of TLS activity.
  • smtpd_tls_mandatory_ciphers (medium) — The minimum TLS cipher grade that the Postfix SMTP server will use with mandatory TLS encryption.
  • 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.
  • smtpd_tls_mandatory_protocols (see 'postconf -d' output) — TLS protocols accepted by the Postfix SMTP server with mandatory TLS encryption.
  • 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. 📨
  • smtpd_tls_req_ccert (no) — With mandatory TLS encryption, require a trusted remote SMTP client certificate in order to allow TLS connections to proceed.
  • 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 in order 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 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) — TLS protocols accepted by the Postfix SMTP server with opportunistic TLS encryption.
  • smtpd_tls_ciphers (medium) — The minimum TLS cipher grade that 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 used by the Postfix SMTP server for sensibly strong ephemeral ECDH key exchange.
  • tls_eecdh_ultra_curve (secp384r1) — The elliptic curve used by the Postfix SMTP server for maximally strong ephemeral ECDH key exchange. 🌈

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.
  • 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) — 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 supported by 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 shutting down a TLS session, until Postfix times out.

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 passed by Postfix to OpenSSL library initialization functions.

🌈 OBSOLETE STARTTLS CONTROLS 🌈

⚠️ these parameters are only here for compatibility with Postfix versions before 2.3. Support for these will be removed in a future release. so like, don't build new stuff on them, bestie 💀
  • smtpd_use_tls (no) — Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but do not require that clients use TLS encryption.
  • smtpd_enforce_tls (no) — Mandatory TLS: announce STARTTLS support to remote SMTP clients, and require that clients use TLS encryption.
  • smtpd_tls_cipherlist (empty) — Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher list.

💜 SMTPUTF8 CONTROLS 💜

Preliminary SMTPUTF8 support is introduced with Postfix 3.0. (yes, preliminary, it's giving early access ✨)

  • 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.
  • 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 is used for DNS lookups. 🌐

🦋 VERP SUPPORT CONTROLS 🦋

okay so with VERP style delivery, 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

okay bestie, when stuff goes sideways and you're like "why is my mail doing THAT 😭", this is the section. The DEBUG_README document spills all the tea on how to debug parts of the Postfix mail system. The methods range from just making the software log a LOT of detail, all the way to running some daemon processes under the control of a call tracer or a debugger. pick your fighter ✨

  • debug_peer_level (default: 2) — how much the verbose logging level gets bumped up when a nexthop destination, remote client or server name, or network address matches a pattern you gave in the debug_peer_list parameter.
  • debug_peer_list (default: empty) — optional list of nexthop destination, remote client or server name, or network address patterns that, if matched, make the verbose logging level go up by however much $debug_peer_level says. it's giving "watch this one specifically" energy 🔍
  • error_notice_recipient (default: postmaster) — who receives postmaster notifications about mail delivery problems caused by policy, resource, software or protocol errors.
  • internal_mail_filter_classes (default: empty) — which categories of Postfix-generated mail get subjected to before-queue content inspection by non_smtpd_milters, header_checks and body_checks.
  • notify_classes (default: resource, software) — the list of error classes that get reported to the postmaster.
  • smtpd_reject_footer (default: empty) — optional info that gets appended after each Postfix SMTP server 4XX or 5XX response.
  • soft_bounce (default: no) — a safety net that keeps mail queued that would otherwise be returned to the sender.

Available in Postfix version 2.1 and later:

  • smtpd_authorized_xclient_hosts (default: empty) — which remote SMTP clients are allowed to use the XCLIENT feature. 🎟️

Available in Postfix version 2.10 and later:

  • smtpd_log_access_permit_actions (default: empty) — turns on logging of the named "permit" actions in SMTP server access lists. and yeah, by default the SMTP server logs "reject" actions but not "permit" actions, so if you're wondering why your permits are silent, that's why bestie 💅

👻 KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS

so as of Postfix version 2.0, the SMTP server rejects mail for unknown recipients. why? because it stops the mail queue from clogging up with undeliverable MAILER-DAEMON messages. it's self care fr fr 🧖 If you want the whole deep dive, LOCAL_RECIPIENT_README and ADDRESS_CLASS_README are right there waiting for you.

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

📍 Parameters concerning known/unknown local recipients

  • mydestination (default: $myhostname, localhost.$mydomain, localhost) — the list of domains that get delivered via the $local_transport mail delivery transport.
  • inet_interfaces (default: all) — the local network interface addresses that this mail system receives mail on.
  • proxy_interfaces (default: empty) — the remote network interface addresses that this mail system receives mail on by way of a proxy or network address translation unit. sneaky but valid 🌐
  • inet_protocols (default: see postconf -d output) — the Internet protocols Postfix will attempt to use when making or accepting connections.
  • local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps) — lookup tables with all names or addresses of local recipients. a recipient address counts as local when its domain matches $mydestination, $inet_interfaces or $proxy_interfaces.
  • unknown_local_recipient_reject_code (default: 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. rude, but the code says so 😤

🛰️ Parameters concerning known/unknown recipients of relay destinations

  • relay_domains (default: Postfix >= 3.0: empty, Postfix < 3.0: $mydestination) — what destination domains (and subdomains thereof) this system will relay mail to.
  • relay_recipient_maps (default: empty) — optional lookup tables with all valid addresses in the domains that match $relay_domains.
  • unknown_relay_recipient_reject_code (default: 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 (default: $virtual_alias_maps) — Postfix is the final destination for the specified list of virtual alias domains. meaning: domains for which all addresses are aliased to addresses in other local or remote domains.
  • virtual_alias_maps (default: $virtual_maps) — optional lookup tables that alias specific mail addresses or domains to other local or remote addresses.
  • unknown_virtual_alias_reject_code (default: 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 (default: $virtual_mailbox_maps) — Postfix is the final destination for the specified list of domains; mail gets delivered via the $virtual_transport mail delivery transport.
  • virtual_mailbox_maps (default: empty) — optional lookup tables with all valid addresses in the domains that match $virtual_mailbox_domains.
  • unknown_virtual_mailbox_reject_code (default: 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.
bestie reminder: those three reject codes all defaulting to 550 is not a coincidence, it's the "no thanks, unknown recipient" flex 💅

🌈 RESOURCE AND RATE CONTROLS 🌈

Okay bestie, these parameters are the bouncers of the SMTP server — they cap how much resource it'll burn and how fast any one client gets to go. Rate limiting era, fr fr. 💅

  • line_length_limit (default 2048) — when stuff comes in, long lines get chopped into lil pieces of at most this length; when it goes back out for delivery, the long lines get stitched back together. Chop chop, sew sew. 🧵
  • queue_minfree (default 0) — the minimum amount of free space, in bytes, that the queue file system needs to have before it'll even accept mail. No room, no mail.
  • message_size_limit (default 10240000) — the biggest a message can be, in bytes, envelope info included. Absolute unit ceiling.
  • smtpd_recipient_limit (default 1000) — the most recipients the Postfix SMTP server will take per message delivery request.
  • smtpd_timeout (default: normal 300s, overload 10s) — two vibes in one: when the server wants to send an SMTP response, this is how long it waits for the underlying network write to finish; and when the server 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 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, and verify the name actually matches the client IP address. Spoiler: names lie sometimes.

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

  • smtpd_client_connection_count_limit (default 50) — how many simultaneous connections any one client is allowed to make to this service. Sharing is caring, bestie.
  • smtpd_client_connection_rate_limit (default 0) — the max number of connection attempts any client can 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 to this service per time unit, regardless of whether Postfix actually accepts those messages. Doesn't matter if it gets rejected, it still counts.
  • smtpd_client_recipient_rate_limit (default 0) — the max number of recipient addresses any client can send to this service per time unit, regardless of whether Postfix actually accepts those recipients.
  • smtpd_client_event_limit_exceptions (default $mynetworks) — the clients that are exempt from the smtpd_client_*_count/rate_limit restrictions. VIP list. 🎀

✨ Available in Postfix version 2.3 and later ✨

  • smtpd_client_new_tls_session_rate_limit (default 0) — the max number of brand-new (i.e., uncached) TLS sessions a remote SMTP client can negotiate with this service per time unit. Fresh TLS only, no reusing, okay? 🔐

✨ Available in Postfix version 2.9 - 3.6 ✨

  • smtpd_per_record_deadline (default: normal no, overload yes) — switches up how the smtpd_timeout and smtpd_starttls_timeout time limits behave: instead of a time limit per read or write system call, it becomes a time limit to send or receive a complete record — that's an SMTP command line, an SMTP response line, an SMTP message content line, or a TLS protocol message. Whole record or nothing.

✨ 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. Stop brute-forcing, it's not cute. 💀

✨ 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: instead of a time limit per plaintext or TLS read/write call, it's a combined time limit for receiving a whole SMTP request AND sending a whole SMTP response. Two-for-one deadline.
  • smtpd_min_data_rate (default 500) — the minimum plaintext data transfer rate in bytes/second for DATA and BDAT requests, when deadlines are enabled via smtpd_per_request_deadline. Speed check: pass or perish.
  • 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 smtpd_client_*_count and smtpd_client_*_rate statistics by IPv4 network blocks with the specified network prefix.
  • smtpd_client_ipv6_prefix_length (default 84) — aggregates smtpd_client_*_count and smtpd_client_*_rate statistics by IPv6 network blocks with the specified network prefix. IPv6 girlies, this one's for you. 🦋

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

  • smtpd_forbid_unauth_pipelining (default: yes on Postfix >= 3.9) — disconnects remote SMTP clients that violate RFC 2920 (or 5321) command pipelining constraints. Rule broken, connection broken. Periodt. 🚫

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

  • smtpd_forbid_bare_newline (default: no on Postfix < 3.9) — reject or restrict input lines from an SMTP client that end in <LF> instead of the standard <CR><LF>. Read the spec, bestie.
  • smtpd_forbid_bare_newline_exclusions (default $mynetworks) — clients to exclude from smtpd_forbid_bare_newline enforcement. Special lil exemption 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 here's the tea: when a remote SMTP client keeps making errors, the Postfix SMTP server can slide in lil delays before responding. It's not petty, it's strategy — it helps slow down runaway software. The whole thing is governed by an error counter that tallies how many errors a client racks up within an SMTP session without delivering mail. You're on thin ice, and the ice is melting on purpose. 🧊

  • smtpd_error_sleep_time (default 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 (default 10) — the number of errors a remote SMTP client can make without delivering mail before the Postfix SMTP server starts slowing down all its responses. Warning shot, bestie.
  • smtpd_hard_error_limit (default: normal 20, overload 1) — the absolute max number of errors a remote SMTP client can make without delivering mail.
  • 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 with each junk command. Filler commands are NOT it.

✨ 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 extra recipient. Over the limit? That's a point against you, every single time.

🫶 ACCESS POLICY DELEGATION CONTROLS 🫶

As of version 2.1, Postfix can be configured to delegate access policy decisions to an external server running outside of Postfix. Outsourcing the judgment calls, iconic. Peep the file SMTPD_POLICY_README for the whole story. 📖

  • smtpd_policy_service_max_idle (default 300s) — how long until an idle SMTPD policy service connection gets closed. Ghost them after 5 minutes.
  • smtpd_policy_service_max_ttl (default 1000s) — how long until 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. No answer? You get a 451, sorry bestie.
  • 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. Two strikes, then we move on.
  • 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 puts in the "policy_context" attribute of a policy service request (originally, this was so multiple check_policy_service clients could share the same service endpoint). Sharing is caring, again. 🫶

💖 ACCESS CONTROLS 💖

okay so bestie, the SMTPD_ACCESS_README document gives an introduction to all the SMTP server access control features. that's the whole vibe. go read it. 💅

  • smtpd_delay_reject (default: yes) — wait until the RCPT TO command before evaluating $smtpd_client_restrictions, $smtpd_helo_restrictions and $smtpd_sender_restrictions, or wait until the ETRN command before evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions. no cap. ✨
  • parent_domain_matches_subdomains (default: 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. iconic behavior. 🦋
  • smtpd_client_restrictions (default: empty) — optional restrictions that the Postfix SMTP server applies in the context of a client connection request. 🌸
  • smtpd_helo_required (default: 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. 💅
  • smtpd_helo_restrictions (default: empty) — optional restrictions that the Postfix SMTP server applies in the context of a client HELO command. ✨
  • smtpd_sender_restrictions (default: empty) — optional restrictions that the Postfix SMTP server applies in the context of a client MAIL FROM command. 💌
  • smtpd_recipient_restrictions (default: 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. 🎀
  • smtpd_etrn_restrictions (default: empty) — optional restrictions that the Postfix SMTP server applies in the context of a client ETRN command. 🌈
  • allow_untrusted_routing (default: no) — forward mail with sender-specified routing (user[@%!]remote[@%!]site) from untrusted clients to destinations matching $relay_domains. lowkey spicy. 🔥
  • smtpd_restriction_classes (default: empty) — user-defined aliases for groups of access restrictions. 💖
  • 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, before smtpd_recipient_restrictions. main character energy fr fr. 👑

🦋 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. it 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. bestie, this is the detective arc. 🔍💖

  • 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 in progress. ✨
  • address_verify_poll_delay (default: 3s) — the delay between queries for the completion of an address verification request in progress. 🎀
  • address_verify_sender (default: $double_bounce_sender) — the sender address to use in address verification probes; prior to Postfix 2.5 the default was "postmaster". 💌
  • 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. yes, it says recipient address, keep it moving. 😭
  • 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. ⭐

👑 ACCESS CONTROL RESPONSES 👑

the following parameters control numerical SMTP reply codes and/or text responses. so like, the actual clapback energy. 💅

  • 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 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 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 junk drawer but make it cute — every random knob that didn't fit anywhere else. 💅

  • config_directory (see postconf -d output) — where the Postfix main.cf and master.cf config files live by default. Your home base, fr.
  • daemon_timeout (18000s) — how long a Postfix daemon process can sit there handling one request before a built-in watchdog timer just... ends it. 18000 seconds of patience, then it's over 💀
  • command_directory (see postconf -d output) — where all the postfix admin commands hang out.
  • double_bounce_sender (double-bounce) — the sender address on postmaster notifications that the mail system itself generates.
  • ipc_timeout (3600s) — the time limit for sending or receiving info over an internal communication channel.
  • mail_name (Postfix) — the mail system name that shows up in Received: headers, in the SMTP greeting banner, and in bounced mail. It's giving branding. 👑
  • mail_owner (postfix) — the UNIX system account that owns the Postfix queue and most Postfix daemon processes.
  • max_idle (100s) — the max time an idle Postfix daemon process waits for an incoming connection before it dips voluntarily. ✌️
  • max_use (100) — the max number of incoming connections a Postfix daemon process will serve before dipping voluntarily. (Yes, "maximal", we love a dramatic word.)
  • myhostname (see postconf -d output) — the internet hostname of this mail system.
  • mynetworks (see postconf -d output) — the list of "trusted" remote SMTP clients that get more privileges than the "strangers". VIP list only, no cap. 🎀
  • myorigin ($myhostname) — the domain name that locally-posted mail appears to come from, and that locally posted mail gets delivered to.
  • process_id (read-only) — the process ID of a Postfix command or daemon process. Look but don't touch, bestie.
  • process_name (read-only) — the process name of a Postfix command or daemon process.
  • queue_directory (see postconf -d output) — where the Postfix top-level queue directory lives.
  • recipient_delimiter (empty) — the set of characters that can separate an email address localpart, user name, or a .forward file name from its extension.
  • smtpd_banner ($myhostname ESMTP $mail_name) — the text that follows the 220 status code in the SMTP greeting banner. First impression energy, literally.
  • syslog_facility (mail) — the syslog facility for Postfix logging.
  • syslog_name (see postconf -d output) — a prefix prepended to the process name in syslog records, so that, for example, "smtpd" becomes "prefix/smtpd". Cute little name tag. 🏷️

✨ Available in Postfix version 2.2 and later: ✨

  • smtpd_forbidden_commands (CONNECT GET POST regexp:{{/^[^A-Z]/ Bogus}}) — list of commands that make the Postfix SMTP server immediately terminate the session with a 221 code. Say the wrong thing and you're out the door, periodt. 🚪

✨ Available in Postfix version 2.5 and later: ✨

  • smtpd_client_port_logging (no) — turn on logging of the remote SMTP client port, on top of 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.

✨ 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. Custom rejection drip, iykyk. 💅

🌈 SEE ALSO 🌈

The friends-of-the-page list, aka the lore you should go read next:

📚 README FILES 📚

Wanna find these? Use "postconf readme_directory" or "postconf html_directory" to locate this information. Slay, go get your reading list. 🫶

  • 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. Not optional, bestie — it ships with it or it doesn't ship. 💖

👑 AUTHOR(S) 👑

The literal icons who built 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

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 SMTPD(8postfix), bestie — the source is the Postfix SMTPD manpage, and its footer date/version stamp is baked right in down at the bottom. Go forth and slay your mail server config, ily 💖✨🎀🦋🌸💅🫶

📦 where this page comes from