SMTP(8)                                                                SMTP(8)

NAME
       smtp - Postfix SMTP+LMTP client

SYNOPSIS
       smtp [generic Postfix daemon options]

DESCRIPTION
       The Postfix SMTP+LMTP client implements the SMTP and LMTP mail delivery
       protocols. It processes message delivery requests from the  queue  man‐
       ager.  Each  request specifies a queue file, a sender address, a domain
       or host to deliver to, and recipient information.  This program expects
       to be run from the master(8) process manager.

       The  SMTP+LMTP  client  updates  the queue file and marks recipients as
       finished, or it informs the queue manager that delivery should be tried
       again  at  a  later  time.  Delivery  status  reports  are  sent to the
       bounce(8), defer(8) or trace(8) daemon as appropriate.

       The SMTP+LMTP client looks up a list of mail  exchanger  addresses  for
       the  destination  host,  sorts  the list by preference, and connects to
       each listed address until it finds a server that responds.

       When a server is not reachable, or when mail delivery fails  due  to  a
       recoverable  error  condition, the SMTP+LMTP client will try to deliver
       the mail to an alternate host.

       After a successful mail transaction, a connection may be saved  to  the
       scache(8)  connection  cache  server,  so  that  it  may be used by any
       SMTP+LMTP client for a subsequent transaction.

       By default, connection caching is enabled temporarily for  destinations
       that have a high volume of mail in the active queue. Connection caching
       can be enabled permanently for specific destinations.

SMTP DESTINATION SYNTAX
       SMTP destinations have the following form:

       domainname

       domainname:port
              Look up the mail exchangers for the specified domain,  and  con‐
              nect to the specified port (default: smtp).

       [hostname]

       [hostname]:port
              Look  up  the  address(es) of the specified host, and connect to
              the specified port (default: smtp).

       [address]

       [address]:port
              Connect to the host at the specified address, and connect to the
              specified  port (default: smtp). An IPv6 address must be format‐
              ted as [ipv6:address].

LMTP DESTINATION SYNTAX
       LMTP destinations have the following form:

       unix:pathname
              Connect to the local UNIX-domain server that  is  bound  to  the
              specified  pathname.  If  the process runs chrooted, an absolute
              pathname is interpreted relative to the Postfix queue directory.

       inet:hostname

       inet:hostname:port

       inet:[address]

       inet:[address]:port
              Connect  to  the  specified  TCP  port on the specified local or
              remote host. If no  port  is  specified,  connect  to  the  port
              defined  as  lmtp  in services(4).  If no such service is found,
              the lmtp_tcp_port configuration parameter (default value of  24)
              will   be   used.    An   IPv6  address  must  be  formatted  as
              [ipv6:address].

SECURITY
       The SMTP+LMTP client is moderately security-sensitive. It talks to SMTP
       or LMTP servers and to DNS servers on the network. The SMTP+LMTP client
       can be run chrooted at fixed low privilege.

STANDARDS
       RFC 821 (SMTP protocol)
       RFC 822 (ARPA Internet Text Messages)
       RFC 1651 (SMTP service extensions)
       RFC 1652 (8bit-MIME transport)
       RFC 1870 (Message Size Declaration)
       RFC 2033 (LMTP protocol)
       RFC 2034 (SMTP Enhanced Error Codes)
       RFC 2045 (MIME: Format of Internet Message Bodies)
       RFC 2046 (MIME: Media Types)
       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 4954 (AUTH command)
       RFC 5321 (SMTP protocol)
       RFC 6531 (Internationalized SMTP)
       RFC 6533 (Internationalized Delivery Status Notifications)

DIAGNOSTICS
       Problems and transactions are logged to syslogd(8).  Corrupted  message
       files are marked so that the queue manager can move them to the corrupt
       queue for further inspection.

       Depending on the setting of the notify_classes parameter, the  postmas‐
       ter is notified of bounces, protocol problems, and of other trouble.

BUGS
       SMTP  and LMTP connection caching does not work with TLS. The necessary
       support for TLS object passivation and  re-activation  does  not  exist
       without closing the session, which defeats the purpose.

       SMTP  and  LMTP  connection  caching  assumes that SASL credentials are
       valid for all destinations that map onto the same IP  address  and  TCP
       port.

CONFIGURATION PARAMETERS
       Before  Postfix version 2.3, the LMTP client is a separate program that
       implements only a subset of  the  functionality  available  with  SMTP:
       there  is  no  support  for TLS, and connections are cached in-process,
       making it ineffective when the client is used for multiple domains.

       Most smtp_xxx configuration parameters have an lmtp_xxx "mirror" param‐
       eter  for  the  equivalent  LMTP  feature. This document describes only
       those LMTP-related parameters that aren't simply "mirror" parameters.

       Changes to main.cf are picked up automatically,  as  smtp(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
       ignore_mx_lookup_error (no)
              Ignore DNS MX lookups that produce no response.

       smtp_always_send_ehlo (yes)
              Always send EHLO at the start of an SMTP session.

       smtp_never_send_ehlo (no)
              Never send EHLO at the start of an SMTP session.

       smtp_defer_if_no_mx_address_found (no)
              Defer mail delivery when no MX record resolves to an IP address.

       smtp_line_length_limit (998)
              The maximal length of message header and body lines that Postfix
              will send via SMTP.

       smtp_pix_workaround_delay_time (10s)
              How   long   the  Postfix  SMTP  client  pauses  before  sending
              ".<CR><LF>"  in  order  to  work   around   the   PIX   firewall
              "<CR><LF>.<CR><LF>" bug.

       smtp_pix_workaround_threshold_time (500s)
              How long a message must be queued before the Postfix SMTP client
              turns on the PIX firewall "<CR><LF>.<CR><LF>" bug workaround for
              delivery through firewalls with "smtp fixup" mode turned on.

       smtp_pix_workarounds (disable_esmtp, delay_dotcrlf)
              A  list  that  specifies  zero or more workarounds for CISCO PIX
              firewall bugs.

       smtp_pix_workaround_maps (empty)
              Lookup tables, indexed by the remote SMTP server  address,  with
              per-destination workarounds for CISCO PIX firewall bugs.

       smtp_quote_rfc821_envelope (yes)
              Quote  addresses  in  Postfix  SMTP client MAIL FROM and RCPT TO
              commands as required by RFC 5321.

       smtp_reply_filter (empty)
              A mechanism to transform replies from remote  SMTP  servers  one
              line at a time.

       smtp_skip_5xx_greeting (yes)
              Skip remote SMTP servers that greet with a 5XX status code.

       smtp_skip_quit_response (yes)
              Do not wait for the response to the SMTP QUIT command.

       Available in Postfix version 2.0 and earlier:

       smtp_skip_4xx_greeting (yes)
              Skip  SMTP  servers  that greet with a 4XX status code (go away,
              try again later).

       Available in Postfix version 2.2 and later:

       smtp_discard_ehlo_keyword_address_maps (empty)
              Lookup tables, indexed by the remote SMTP server  address,  with
              case  insensitive  lists of EHLO keywords (pipelining, starttls,
              auth, etc.) that the Postfix SMTP client will ignore in the EHLO
              response from a remote SMTP server.

       smtp_discard_ehlo_keywords (empty)
              A  case insensitive list of EHLO keywords (pipelining, starttls,
              auth, etc.) that the Postfix SMTP client will ignore in the EHLO
              response from a remote SMTP server.

       smtp_generic_maps (empty)
              Optional  lookup  tables  that  perform address rewriting in the
              Postfix SMTP client, typically  to  transform  a  locally  valid
              address  into  a globally valid address when sending mail across
              the Internet.

       Available in Postfix version 2.2.9 and later:

       smtp_cname_overrides_servername (version dependent)
              When the remote SMTP servername is  a  DNS  CNAME,  replace  the
              servername  with the result from CNAME expansion for the purpose
              of logging, SASL password lookup, TLS policy decisions,  or  TLS
              certificate verification.

       Available in Postfix version 2.3 and later:

       lmtp_discard_lhlo_keyword_address_maps (empty)
              Lookup  tables,  indexed by the remote LMTP server address, with
              case insensitive lists of LHLO keywords  (pipelining,  starttls,
              auth, etc.) that the Postfix LMTP client will ignore in the LHLO
              response from a remote LMTP server.

       lmtp_discard_lhlo_keywords (empty)
              A case insensitive list of LHLO keywords (pipelining,  starttls,
              auth, etc.) that the Postfix LMTP client will ignore in the LHLO
              response from a remote LMTP server.

       Available in Postfix version 2.4.4 and later:

       send_cyrus_sasl_authzid (no)
              When authenticating to a remote SMTP or  LMTP  server  with  the
              default  setting  "no", send no SASL authoriZation ID (authzid);
              send only the SASL authentiCation ID (authcid)  plus  the  auth‐
              cid's password.

       Available in Postfix version 2.5 and later:

       smtp_header_checks (empty)
              Restricted  header_checks(5) tables for the Postfix SMTP client.

       smtp_mime_header_checks (empty)
              Restricted mime_header_checks(5) tables  for  the  Postfix  SMTP
              client.

       smtp_nested_header_checks (empty)
              Restricted  nested_header_checks(5)  tables for the Postfix SMTP
              client.

       smtp_body_checks (empty)
              Restricted body_checks(5) tables for the Postfix SMTP client.

       Available in Postfix version 2.6 and later:

       tcp_windowsize (0)
              An optional workaround for routers that break TCP  window  scal‐
              ing.

       Available in Postfix version 2.8 and later:

       smtp_dns_resolver_options (empty)
              DNS Resolver options for the Postfix SMTP client.

       Available in Postfix version 2.9 and later:

       smtp_per_record_deadline (no)
              Change  the  behavior  of the smtp_*_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  mes‐
              sage).

       smtp_send_dummy_mail_auth (no)
              Whether  or  not to append the "AUTH=<>" option to the MAIL FROM
              command in SASL-authenticated SMTP sessions.

       Available in Postfix version 2.11 and later:

       smtp_dns_support_level (empty)
              Level of DNS support in the Postfix SMTP client.

       Available in Postfix version 2.12 and later:

       smtp_delivery_status_filter ($default_delivery_status_filter)
              Optional filter for the smtp(8) delivery  agent  to  change  the
              delivery status code or explanatory text of successful or unsuc‐
              cessful deliveries.

MIME PROCESSING CONTROLS
       Available in Postfix version 2.0 and later:

       disable_mime_output_conversion (no)
              Disable the conversion of 8BITMIME format to 7BIT format.

       mime_boundary_length_limit (2048)
              The maximal length of MIME multipart boundary strings.

       mime_nesting_limit (100)
              The maximal recursion level that the MIME processor will handle.

EXTERNAL CONTENT INSPECTION CONTROLS
       Available in Postfix version 2.1 and later:

       smtp_send_xforward_command (no)
              Send  the  non-standard  XFORWARD  command when the Postfix SMTP
              server EHLO response announces XFORWARD support.

SASL AUTHENTICATION CONTROLS
       smtp_sasl_auth_enable (no)
              Enable SASL authentication in the Postfix SMTP client.

       smtp_sasl_password_maps (empty)
              Optional Postfix  SMTP  client  lookup  tables  with  one  user‐
              name:password  entry  per  remote  hostname or domain, or sender
              address when sender-dependent authentication is enabled.

       smtp_sasl_security_options (noplaintext, noanonymous)
              Postfix SMTP client SASL security options; as of Postfix 2.3 the
              list  of available features depends on the SASL client implemen‐
              tation that is selected with smtp_sasl_type.

       Available in Postfix version 2.2 and later:

       smtp_sasl_mechanism_filter (empty)
              If non-empty, a Postfix SMTP client filter for the  remote  SMTP
              server's list of offered SASL mechanisms.

       Available in Postfix version 2.3 and later:

       smtp_sender_dependent_authentication (no)
              Enable  sender-dependent  authentication  in  the  Postfix  SMTP
              client; this is available only  with  SASL  authentication,  and
              disables  SMTP  connection caching to ensure that mail from dif‐
              ferent senders will use the appropriate credentials.

       smtp_sasl_path (empty)
              Implementation-specific information that the Postfix SMTP client
              passes  through  to  the  SASL  plug-in  implementation  that is
              selected with smtp_sasl_type.

       smtp_sasl_type (cyrus)
              The SASL plug-in type that the Postfix SMTP  client  should  use
              for authentication.

       Available in Postfix version 2.5 and later:

       smtp_sasl_auth_cache_name (empty)
              An  optional table to prevent repeated SASL authentication fail‐
              ures with the same remote SMTP  server  hostname,  username  and
              password.

       smtp_sasl_auth_cache_time (90d)
              The  maximal age of an smtp_sasl_auth_cache_name entry before it
              is removed.

       smtp_sasl_auth_soft_bounce (yes)
              When a remote SMTP server rejects a SASL authentication  request
              with  a 535 reply code, defer mail delivery instead of returning
              mail as undeliverable.

       Available in Postfix version 2.9 and later:

       smtp_send_dummy_mail_auth (no)
              Whether or not to append the "AUTH=<>" option to the  MAIL  FROM
              command in SASL-authenticated SMTP sessions.

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

       smtp_tls_security_level (empty)
              The default SMTP TLS security level for the Postfix SMTP client;
              when a non-empty value is specified, this overrides the obsolete
              parameters       smtp_use_tls,       smtp_enforce_tls,       and
              smtp_tls_enforce_peername.

       smtp_sasl_tls_security_options ($smtp_sasl_security_options)
              The  SASL  authentication security options that the Postfix SMTP
              client uses for TLS encrypted SMTP sessions.

       smtp_starttls_timeout (300s)
              Time limit for Postfix SMTP client  write  and  read  operations
              during TLS startup and shutdown handshake procedures.

       smtp_tls_CAfile (empty)
              A  file  containing  CA certificates of root CAs trusted to sign
              either remote SMTP server certificates or intermediate  CA  cer‐
              tificates.

       smtp_tls_CApath (empty)
              Directory  with  PEM  format  certificate authority certificates
              that the Postfix SMTP client uses to verify a remote SMTP server
              certificate.

       smtp_tls_cert_file (empty)
              File with the Postfix SMTP client RSA certificate in PEM format.

       smtp_tls_mandatory_ciphers (medium)
              The minimum TLS cipher grade that the Postfix SMTP  client  will
              use with mandatory TLS encryption.

       smtp_tls_exclude_ciphers (empty)
              List of ciphers or cipher types to exclude from the Postfix SMTP
              client cipher list at all TLS security levels.

       smtp_tls_mandatory_exclude_ciphers (empty)
              Additional list of ciphers or cipher types to exclude  from  the
              Postfix  SMTP  client cipher list at mandatory TLS security lev‐
              els.

       smtp_tls_dcert_file (empty)
              File with the Postfix SMTP client DSA certificate in PEM format.

       smtp_tls_dkey_file ($smtp_tls_dcert_file)
              File with the Postfix SMTP client DSA private key in PEM format.

       smtp_tls_key_file ($smtp_tls_cert_file)
              File with the Postfix SMTP client RSA private key in PEM format.

       smtp_tls_loglevel (0)
              Enable additional Postfix SMTP client logging of TLS activity.

       smtp_tls_note_starttls_offer (no)
              Log  the  hostname of a remote SMTP server that offers STARTTLS,
              when TLS is not already enabled for that server.

       smtp_tls_policy_maps (empty)
              Optional lookup tables with the Postfix SMTP client TLS security
              policy by next-hop destination; when a non-empty value is speci‐
              fied, this overrides the obsolete smtp_tls_per_site parameter.

       smtp_tls_mandatory_protocols (!SSLv2)
              List of SSL/TLS protocols that the Postfix SMTP client will  use
              with mandatory TLS encryption.

       smtp_tls_scert_verifydepth (9)
              The verification depth for remote SMTP server certificates.

       smtp_tls_secure_cert_match (nexthop, dot-nexthop)
              How  the  Postfix  SMTP  client  verifies the server certificate
              peername for the "secure" TLS security level.

       smtp_tls_session_cache_database (empty)
              Name of the file containing the optional Postfix SMTP client TLS
              session cache.

       smtp_tls_session_cache_timeout (3600s)
              The  expiration  time  of  Postfix SMTP client TLS session cache
              information.

       smtp_tls_verify_cert_match (hostname)
              How the Postfix SMTP  client  verifies  the  server  certificate
              peername for the "verify" TLS security level.

       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 2.4 and later:

       smtp_sasl_tls_verified_security_options           ($smtp_sasl_tls_secu‐‐
       rity_options)
              The SASL authentication security options that the  Postfix  SMTP
              client  uses  for  TLS  encrypted  SMTP sessions with a verified
              server certificate.

       Available in Postfix version 2.5 and later:

       smtp_tls_fingerprint_cert_match (empty)
              List of acceptable remote SMTP server  certificate  fingerprints
              for   the   "fingerprint"  TLS  security  level  (smtp_tls_secu‐‐
              rity_level = fingerprint).

       smtp_tls_fingerprint_digest (md5)
              The message digest  algorithm  used  to  construct  remote  SMTP
              server certificate fingerprints.

       Available in Postfix version 2.6 and later:

       smtp_tls_protocols (!SSLv2)
              List  of TLS protocols that the Postfix SMTP client will exclude
              or include with opportunistic TLS encryption.

       smtp_tls_ciphers (export)
              The minimum TLS cipher grade that the Postfix SMTP  client  will
              use with opportunistic TLS encryption.

       smtp_tls_eccert_file (empty)
              File  with the Postfix SMTP client ECDSA certificate in PEM for‐
              mat.

       smtp_tls_eckey_file ($smtp_tls_eccert_file)
              File with the Postfix SMTP client ECDSA private key in PEM  for‐
              mat.

       Available in Postfix version 2.7 and later:

       smtp_tls_block_early_mail_reply (no)
              Try  to  detect  a mail hijacking attack based on a TLS protocol
              vulnerability (CVE-2009-3555), where an attacker prepends  mali‐
              cious  HELO,  MAIL, RCPT, DATA commands to a Postfix SMTP client
              TLS session.

       Available in Postfix version 2.8 and later:

       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:

       smtp_tls_trust_anchor_file (empty)
              Zero or more PEM-format  files  with  trust-anchor  certificates
              and/or public keys.

       smtp_tls_force_insecure_host_tlsa_lookup (no)
              Lookup  the  associated  DANE TLSA RRset even when a hostname is
              not an alias and its address records lie in an unsigned zone.

       tls_dane_trust_anchor_digest_enable (yes)
              RFC 6698 trust-anchor digest support in the Postfix TLS library.

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

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.

       smtp_use_tls (no)
              Opportunistic  mode: use TLS when a remote SMTP server announces
              STARTTLS support, otherwise send the mail in the clear.

       smtp_enforce_tls (no)
              Enforcement mode: require  that  remote  SMTP  servers  use  TLS
              encryption, and never send mail in the clear.

       smtp_tls_enforce_peername (yes)
              With  mandatory  TLS  encryption,  require  that the remote SMTP
              server hostname matches  the  information  in  the  remote  SMTP
              server certificate.

       smtp_tls_per_site (empty)
              Optional  lookup  tables  with the Postfix SMTP client TLS usage
              policy by next-hop destination and by remote SMTP  server  host‐
              name.

       smtp_tls_cipherlist (empty)
              Obsolete  Postfix  < 2.3 control for the Postfix SMTP client TLS
              cipher list.

RESOURCE AND RATE CONTROLS
       smtp_destination_concurrency_limit        ($default_destination_concur‐‐
       rency_limit)
              The maximal number of parallel deliveries to the  same  destina‐
              tion via the smtp message delivery transport.

       smtp_destination_recipient_limit ($default_destination_recipient_limit)
              The  maximal  number of recipients per message for the smtp mes‐
              sage delivery transport.

       smtp_connect_timeout (30s)
              The Postfix SMTP client time limit for completing a TCP  connec‐
              tion, or zero (use the operating system built-in time limit).

       smtp_helo_timeout (300s)
              The  Postfix SMTP client time limit for sending the HELO or EHLO
              command, and  for  receiving  the  initial  remote  SMTP  server
              response.

       lmtp_lhlo_timeout (300s)
              The Postfix LMTP client time limit for sending the LHLO command,
              and for receiving the initial remote LMTP server response.

       smtp_xforward_timeout (300s)
              The Postfix SMTP client time limit for sending the XFORWARD com‐
              mand, and for receiving the remote SMTP server response.

       smtp_mail_timeout (300s)
              The  Postfix  SMTP  client  time limit for sending the MAIL FROM
              command, and for receiving the remote SMTP server response.

       smtp_rcpt_timeout (300s)
              The Postfix SMTP client time limit for sending the SMTP RCPT  TO
              command, and for receiving the remote SMTP server response.

       smtp_data_init_timeout (120s)
              The  Postfix  SMTP  client  time limit for sending the SMTP DATA
              command, and for receiving the remote SMTP server response.

       smtp_data_xfer_timeout (180s)
              The Postfix SMTP client time limit for sending the SMTP  message
              content.

       smtp_data_done_timeout (600s)
              The Postfix SMTP client time limit for sending the SMTP ".", and
              for receiving the remote SMTP server response.

       smtp_quit_timeout (300s)
              The Postfix SMTP client time limit for sending the QUIT command,
              and for receiving the remote SMTP server response.

       Available in Postfix version 2.1 and later:

       smtp_mx_address_limit (5)
              The  maximal number of MX (mail exchanger) IP addresses that can
              result from Postfix SMTP client mail exchanger lookups, or  zero
              (no limit).

       smtp_mx_session_limit (2)
              The  maximal number of SMTP sessions per delivery request before
              the Postfix SMTP client gives up  or  delivers  to  a  fall-back
              relay host, or zero (no limit).

       smtp_rset_timeout (20s)
              The Postfix SMTP client time limit for sending the RSET command,
              and for receiving the remote SMTP server response.

       Available in Postfix version 2.2 and earlier:

       lmtp_cache_connection (yes)
              Keep Postfix LMTP client connections open for  up  to  $max_idle
              seconds.

       Available in Postfix version 2.2 and later:

       smtp_connection_cache_destinations (empty)
              Permanently  enable  SMTP  connection  caching for the specified
              destinations.

       smtp_connection_cache_on_demand (yes)
              Temporarily enable SMTP connection caching while  a  destination
              has a high volume of mail in the active queue.

       smtp_connection_reuse_time_limit (300s)
              The amount of time during which Postfix will use an SMTP connec‐
              tion repeatedly.

       smtp_connection_cache_time_limit (2s)
              When SMTP connection caching is enabled, the amount of time that
              an unused SMTP client socket is kept open before it is closed.

       Available in Postfix version 2.3 and later:

       connection_cache_protocol_timeout (5s)
              Time  limit for connection cache connect, send or receive opera‐
              tions.

       Available in Postfix version 2.9 and later:

       smtp_per_record_deadline (no)
              Change the behavior of the smtp_*_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 mes‐
              sage).

       Available in Postfix version 2.11 and later:

       smtp_connection_reuse_count_limit (0)
              When SMTP connection caching is enabled,  the  number  of  times
              that  an SMTP session may be reused before it is closed, or zero
              (no limit).

SMTPUTF8 CONTROLS
       Preliminary SMTPUTF8 support is introduced with Postfix 2.12.

       smtputf8_enable (no)
              Enable experimental SMTPUTF8 support for the protocols described
              in RFC 6531..6533.

       smtputf8_autodetect_classes (sendmail, verify)
              Enable  SMTPUTF8  autodetection  for  the  specified mail origin
              classes.

TROUBLE SHOOTING CONTROLS
       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 proto‐
              col 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.

MISCELLANEOUS CONTROLS
       best_mx_transport (empty)
              Where  the  Postfix  SMTP  client  should  deliver  mail when it
              detects a "mail loops back to myself" error condition.

       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and  master.cf  con‐
              figuration 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.

       delay_logging_resolution_limit (2)
              The maximal number of digits after the decimal point  when  log‐
              ging sub-second delay values.

       disable_dns_lookups (no)
              Disable DNS lookups in the Postfix SMTP and LMTP clients.

       inet_interfaces (all)
              The  network  interface addresses that this mail system receives
              mail on.

       inet_protocols (all)
              The Internet protocols Postfix will attempt to use  when  making
              or accepting connections.

       ipc_timeout (3600s)
              The  time  limit  for  sending  or receiving information over an
              internal communication channel.

       lmtp_assume_final (no)
              When a remote LMTP server announces no DSN support, assume  that
              the  server performs final delivery, and send "delivered" deliv‐
              ery status notifications instead of "relayed".

       lmtp_tcp_port (24)
              The default TCP port that the Postfix LMTP client connects to.

       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.

       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.

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

       smtp_address_preference (any)
              The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP
              client  will  try  first,  when  a destination has IPv6 and IPv4
              addresses with equal MX preference.

       smtp_bind_address (empty)
              An optional numerical network  address  that  the  Postfix  SMTP
              client should bind to when making an IPv4 connection.

       smtp_bind_address6 (empty)
              An  optional  numerical  network  address  that the Postfix SMTP
              client should bind to when making an IPv6 connection.

       smtp_helo_name ($myhostname)
              The hostname to send in the SMTP EHLO or HELO command.

       lmtp_lhlo_name ($myhostname)
              The hostname to send in the LMTP LHLO command.

       smtp_host_lookup (dns)
              What mechanisms the Postfix SMTP client uses to look up a host's
              IP address.

       smtp_randomize_addresses (yes)
              Randomize the order of equal-preference MX host addresses.

       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,  "post‐
              fix/smtpd".

       Available with Postfix 2.2 and earlier:

       fallback_relay (empty)
              Optional list of relay hosts for SMTP destinations that can't be
              found or that are unreachable.

       Available with Postfix 2.3 and later:

       smtp_fallback_relay ($fallback_relay)
              Optional list of relay hosts for SMTP destinations that can't be
              found or that are unreachable.

SEE ALSO
       generic(5), output address rewriting
       header_checks(5), message header content inspection
       body_checks(5), body parts content inspection
       qmgr(8), queue manager
       bounce(8), delivery status reports
       scache(8), connection cache server
       postconf(5), configuration parameters
       master(5), generic daemon options
       master(8), process manager
       tlsmgr(8), TLS session and PRNG management
       syslogd(8), system logging

README FILES
       SASL_README, Postfix SASL howto
       TLS_README, Postfix STARTTLS howto

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

       Command pipelining in cooperation with:
       Jon Ribbens
       Oaktree Internet Solutions Ltd.,
       Internet House,
       Canal Basin,
       Coventry,
       CV1 4LY, United Kingdom.

       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 and SMTP connection cache support by:
       Victor Duchovni
       Morgan Stanley

                                                                       SMTP(8)