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SMTPD


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NAME

smtpd

Postfix SMTP server
 

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.
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 be 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.
 

STANDARDS


RFC 821 (SMTP protocol)
RFC 1123 (Host requirements)
RFC 1652 (8bit-MIME transport)
RFC 1869 (SMTP service extensions)
RFC 1870 (Message Size Declaration)
RFC 1985 (ETRN command)
RFC 2034 (SMTP Enhanced Error Codes)
RFC 2554 (AUTH command)
RFC 2821 (SMTP protocol)
RFC 2920 (SMTP Pipelining)
RFC 3207 (STARTTLS command)
RFC 3461 (SMTP DSN Extension)
RFC 3463 (Enhanced Status Codes)
RFC 3848 (ESMTP Transmission Types)
RFC 4954 (AUTH command)
 

DIAGNOSTICS

Problems and transactions are logged to syslogd(8).


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

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.
 

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.


broken_sasl_auth_clients (no)

Enable inter-operability with 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:


resolve_null_domain (no)

Resolve an address that ends in the "@" null domain as if the
local hostname were specified, instead of rejecting the address as
invalid.
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 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 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.

 

ADDRESS REWRITING CONTROLS


See the ADDRESS_REWRITING_README document for a detailed
discussion of Postfix address rewriting.


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 message header addresses in mail from these clients and
update incomplete addresses with the domain name in $myorigin or
$mydomain; either don’t rewrite message headers from other clients
at all, or rewrite message headers and update incomplete addresses
with the domain specified in the remote_header_rewrite_domain
parameter.

 

AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS


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


content_filter (empty)

The name of a mail delivery transport that filters mail after
it is queued.

 

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_timeout (100s)

The time limit for connecting to a proxy filter and for sending or
receiving information.

 

BEFORE QUEUE MILTER CONTROLS


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 can request modifications before
mail is queued. For details 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 and optional protocol extensions
for communication with a Milter application; prior to Postfix 2.6
the default protocol is 2.
milter_default_action (tempfail)

The default action when a Milter (mail filter) application is
unavailable or mis-configured.
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.

 

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 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 inter-operability with 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 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.

 

STARTTLS SUPPORT CONTROLS


Detailed information about STARTTLS configuration may be
found in the TLS_README document.


smtpd_tls_security_level (empty)

The SMTP TLS security level for the Postfix SMTP server; when
a non-empty value is specified, this overrides the obsolete parameters
smtpd_use_tls and smtpd_enforce_tls.
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 (300s)

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.
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 EDH ciphers.
smtpd_tls_dh512_param_file (empty)

File with DH parameters that the Postfix SMTP server should
use with 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
SMTP server cipher list at mandatory TLS security levels.
smtpd_tls_mandatory_protocols (SSLv3, TLSv1)

The SSL/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 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_session_cache_database (empty)

Name of the file containing the optional Postfix SMTP server
TLS session cache.
smtpd_tls_session_cache_timeout (3600s)

The expiration time of Postfix SMTP server TLS session cache
information.
smtpd_tls_wrappermode (no)

Run the Postfix SMTP server in the non-standard "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 (ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)

The OpenSSL cipherlist for "HIGH" grade ciphers.
tls_medium_cipherlist (ALL:!EXPORT:!LOW:+RC4:@STRENGTH)

The OpenSSL cipherlist for "MEDIUM" or higher grade ciphers.
tls_low_cipherlist (ALL:!EXPORT:+RC4:@STRENGTH)

The OpenSSL cipherlist for "LOW" or higher grade ciphers.
tls_export_cipherlist (ALL:+RC4:@STRENGTH)

The OpenSSL cipherlist for "EXPORT" 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 2.5 and later:


smtpd_tls_fingerprint_digest (md5)

The message digest algorithm used to construct client-certificate
fingerprints for check_ccert_access and
permit_tls_clientcerts.

Available in Postfix version 2.6 and later:


smtpd_tls_protocols (empty)

List of TLS protocols that the Postfix SMTP server will exclude
or include with opportunistic TLS encryption.
smtpd_tls_ciphers (export)

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 SMTP server for sensibly strong
ephemeral ECDH key exchange.
tls_eecdh_ultra_curve (secp384r1)

The elliptic curve used by the SMTP server for maximally strong
ephemeral ECDH key exchange.

 

OBSOLETE STARTTLS CONTROLS


The following configuration parameters exist for compatibility
with Postfix versions before 2.3. Support for these will
be removed in a future release.


smtpd_use_tls (no)

Opportunistic TLS: announce STARTTLS support to SMTP clients,
but do not require that clients use TLS encryption.
smtpd_enforce_tls (no)

Mandatory TLS: announce STARTTLS support to 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.

 

VERP SUPPORT CONTROLS


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 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 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.


debug_peer_level (2)

The increment in verbose logging level when a remote client or
server matches a pattern in the debug_peer_list parameter.
debug_peer_list (empty)

Optional list of remote client or server hostname or network
address patterns that 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.
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 SMTP clients are allowed to use the XCLIENT feature.

 

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.

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 network interface addresses that this mail system receives
mail on.
proxy_interfaces (empty)

The network interface addresses that this mail system receives mail
on by way of a proxy or network address translation unit.
inet_protocols (ipv4)

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 local recipients:
a recipient address is local when its domain matches $mydestination,
$inet_interfaces or $proxy_interfaces.
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 ($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 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 alias specific mail addresses or domains
to other local or remote address.
unknown_virtual_alias_reject_code (550)

The 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 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 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


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.
message_size_limit (10240000)

The maximal size in bytes of a message, including envelope information.
smtpd_recipient_limit (1000)

The maximal number of recipients that the Postfix SMTP server
accepts per message delivery request.
smtpd_timeout (normal: 300s, stress: 10s)

The time limit for sending a Postfix SMTP server response and for
receiving a remote SMTP client request.
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 connection count, connection rate,
or SMTP request rate 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.

 

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, stress: 1)

The maximal number of errors a remote SMTP client is allowed to
make without delivering mail.
smtpd_junk_command_limit (normal: 100, stress: 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.

 

ACCESS CONTROLS


The SMTPD_ACCESS_README document gives an introduction to all the
SMTP server access control features.


smtpd_delay_reject (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.
parent_domain_matches_subdomains (see ‘postconf -d’ output)

What Postfix features match subdomains of "domain.tld" automatically,
instead of requiring an explicit ".domain.tld" pattern.
smtpd_client_restrictions (empty)

Optional SMTP server access restrictions in the context of a client
SMTP connection request.
smtpd_helo_required (no)

Require that a remote SMTP client introduces itself at the beginning
of an SMTP session with the HELO or EHLO command.
smtpd_helo_restrictions (empty)

Optional restrictions that the Postfix SMTP server applies in the
context of the SMTP HELO command.
smtpd_sender_restrictions (empty)

Optional restrictions that the Postfix SMTP server applies in the
context of the MAIL FROM command.
smtpd_recipient_restrictions (permit_mynetworks, reject_unauth_destination)

The access restrictions that the Postfix SMTP server applies in
the context of the RCPT TO command.
smtpd_etrn_restrictions (empty)

Optional SMTP server access restrictions in the context of a client
ETRN request.
allow_untrusted_routing (no)

Forward mail with sender-specified routing (user[@%!]remote[@%!]site)
from untrusted clients to destinations matching $relay_domains.
smtpd_restriction_classes (empty)

User-defined aliases for groups of access restrictions.
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.

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_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.

 

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.
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.


address_verify_poll_count (3)

How many times to query the verify(8) service for the completion
of an address verification request in progress.
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".
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.
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.

 

ACCESS CONTROL RESPONSES


The following parameters control numerical SMTP reply codes
and/or text responses.


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_sender or reject_rhsbl_recipient restriction.
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 Postfix SMTP server response code when a sender or
recipient address is rejected by the reject_unknown_sender_domain
or reject_unknown_recipient_domain restriction.
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 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 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".
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 an 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.

 

MISCELLANEOUS CONTROLS



config_directory (see ‘postconf -d’ output)

The default location of the Postfix main.cf and master.cf
configuration files.
daemon_timeout (18000s)

How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.
command_directory (see ‘postconf -d’ output)

The location of all postfix administrative commands.
double_bounce_sender (double-bounce)

The sender address of postmaster notifications that are generated
by the mail system.
ipc_timeout (3600s)

The time limit for sending or receiving information over an internal
communication channel.
mail_name (Postfix)

The mail system name that is displayed in Received: headers, in
the SMTP greeting banner, and in bounced mail.
mail_owner (postfix)

The UNIX system account that owns the Postfix queue and most Postfix
daemon processes.
max_idle (100s)

The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily.
max_use (100)

The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.
myhostname (see ‘postconf -d’ output)

The internet hostname of this mail system.
mynetworks (see ‘postconf -d’ output)

The list of "trusted" SMTP clients that have more privileges than
"strangers".
myorigin ($myhostname)

The domain name that locally-posted mail appears to come
from, and that locally posted mail is delivered to.
process_id (read-only)

The process ID of a Postfix command or daemon process.
process_name (read-only)

The process name of a Postfix command or daemon process.
queue_directory (see ‘postconf -d’ output)

The location of the Postfix top-level queue directory.
recipient_delimiter (empty)

The separator between user names and address extensions (user+foo).
smtpd_banner ($myhostname ESMTP $mail_name)

The text that follows the 220 status code in the SMTP greeting
banner.
syslog_facility (mail)

The syslog facility of Postfix logging.
syslog_name (see ‘postconf -d’ output)

The mail system name that is prepended to the process name in syslog
records, so that "smtpd" becomes, for example, "postfix/smtpd".

Available in Postfix version 2.2 and later:


smtpd_forbidden_commands (CONNECT, GET, POST)

List of commands that causes the Postfix SMTP server to immediately
terminate the session with a 221 code.

Available in Postfix version 2.5 and later:


smtpd_client_port_logging (no)

Enable logging of the remote SMTP client port in addition to
the hostname and IP address.

 

SEE ALSO


anvil(8), connection/rate limiting
cleanup(8), message canonicalization
tlsmgr(8), TLS session and PRNG management
trivial-rewrite(8), address resolver
verify(8), address verification service
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
syslogd(8), system logging
 

README FILES


Use "postconf readme_directory" or
"postconf html_directory" to locate this information.


ADDRESS_CLASS_README, blocking unknown hosted or relay recipients
ADDRESS_REWRITING_README Postfix address manipulation
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.
 

AUTHOR(S)


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




 

Index



NAME

SYNOPSIS

DESCRIPTION

SECURITY

STANDARDS

DIAGNOSTICS

CONFIGURATION PARAMETERS

COMPATIBILITY CONTROLS

ADDRESS REWRITING CONTROLS

AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS

BEFORE QUEUE EXTERNAL CONTENT INSPECTION CONTROLS

BEFORE QUEUE MILTER CONTROLS

GENERAL CONTENT INSPECTION CONTROLS

EXTERNAL CONTENT INSPECTION CONTROLS

SASL AUTHENTICATION CONTROLS

STARTTLS SUPPORT CONTROLS

OBSOLETE STARTTLS CONTROLS

VERP SUPPORT CONTROLS

TROUBLE SHOOTING CONTROLS

KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS

RESOURCE AND RATE CONTROLS

TARPIT CONTROLS

ACCESS POLICY DELEGATION CONTROLS

ACCESS CONTROLS

SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS

ACCESS CONTROL RESPONSES

MISCELLANEOUS CONTROLS

SEE ALSO

README FILES

LICENSE

AUTHOR(S)



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