SMTPD(8)                                                 SMTPD(8)

NAME
       smtpd - Postfix SMTP server

SYNOPSIS
       smtpd [generic Postfix daemon options]

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) dae-
       mon, 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 takes an  established  con-
       nection  on  standard input and deposits messages directly
       into the maildrop queue.  In  this  so-called  stand-alone
       mode,  the SMTP server can accept mail even while the mail
       system is not running.

       The SMTP server implements a variety of policies for  con-
       nection  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 2554 (AUTH command)
       RFC 2821 (SMTP protocol)
       RFC 2920 (SMTP Pipelining)

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
       The  following  main.cf parameters are especially relevant
       to this program. See the Postfix main.cf file  for  syntax
       details  and  for  default  values. Use the postfix reload
       command after a configuration change.

Compatibility controls
       strict_rfc821_envelopes
              Disallow non-RFC 821 style addresses in  SMTP  com-
              mands.  For example, the RFC822-style address forms
              with comments that Sendmail allows.

       broken_sasl_auth_clients
              Support Microsoft clients that implement  an  older
              version  of  the  AUTH protocol, and that expect an
              EHLO response of "250 AUTH=list"  instead  of  "250
              AUTH list".

       smtpd_sasl_exceptions_networks
              Don't offer AUTH in the response to EHLO when talk-
              ing to clients in the specified networks.  This  is
              a  workaround  for clients that that demand a login
              and password from the user whenever AUTH is offered
              by an SMTP server.

       smtpd_noop_commands
              List of commands that are treated as NOOP (no oper-
              ation)  commands,  without  any  parameter   syntax
              checking  and  without any state change.  This list
              overrides built-in command definitions.

Content inspection controls
       Optionally, Postfix can be configured to send new mail  to
       external content filter software AFTER the mail is queued.

       content_filter
              The name of a mail delivery transport that  filters
              mail and that either bounces mail or re-injects the
              result back into Postfix.  This parameter uses  the
              same  syntax  as  the  right-hand side of a Postfix
              transport table.

       receive_override_options
              The following options  override  main.cf  settings.
              The  options  are  either  implemented  by the SMTP
              server or are passed on to the  downstream  cleanup
              server.

              no_unknown_recipient_checks
                     Do  not  try  to  reject unknown recipients.
                     This is typically specified  with  the  SMTP
                     server after an external content filter.

              no_address_mappings
                     Disable  canonical  address mapping, virtual
                     alias map expansion,  address  masquerading,
                     and  automatic BCC recipients. This is typi-
                     cally specified with the SMTP server  before
                     an external content filter.

              no_header_body_checks
                     Disable  header/body_checks.  This  is typi-
                     cally specified with the SMTP  server  after
                     an external content filter.

Pass-through proxy
       Optionally,  the  Postfix SMTP server can be configured to
       forward all mail to a proxy server, for  example  a  real-
       time content filter, BEFORE mail is queued.

       smtpd_proxy_filter
              The host:port of the SMTP proxy server. The host or
              host: portion is optional.

       smtpd_proxy_timeout
              Timeout for connecting to, sending to and receiving
              from the SMTP proxy server.

       smtpd_proxy_ehlo
              The hostname to use when sending an EHLO command to
              the SMTP proxy server.

Authentication controls
       smtpd_sasl_auth_enable
              Enable per-session authentication as per  RFC  2554
              (SASL).   This functionality is available only when
              explicitly  selected  at  program  build  time  and
              explicitly enabled at runtime.

       smtpd_sasl_local_domain
              The name of the local authentication realm.

       smtpd_sasl_security_options
              Zero or more of the following.

              noplaintext
                     Disallow  authentication  methods  that  use
                     plaintext passwords.

              noactive
                     Disallow  authentication  methods  that  are
                     vulnerable to non-dictionary active attacks.

              nodictionary
                     Disallow  authentication  methods  that  are
                     vulnerable to passive dictionary attack.

              noanonymous
                     Disallow anonymous logins.

       smtpd_sender_login_maps
              Maps  that  specify the SASL login name that owns a
              MAIL   FROM   sender   address.   Used    by    the
              reject_sender_login_mismatch  sender  anti-spoofing
              restriction.

Miscellaneous
       authorized_verp_clients
              Hostnames, domain names and/or addresses of clients
              that are authorized to use the XVERP extension.

       debug_peer_level
              Increment  in  verbose  logging level when a remote
              host  matches  a  pattern  in  the  debug_peer_list
              parameter.

       debug_peer_list
              List  of  domain or network patterns. When a remote
              host matches a pattern, increase the  verbose  log-
              ging   level   by   the  amount  specified  in  the
              debug_peer_level parameter.

       default_verp_delimiters
              The default VERP delimiter characters that are used
              when   the   XVERP  command  is  specified  without
              explicit delimiters.

       error_notice_recipient
              Recipient   of    protocol/policy/resource/software
              error notices.

       hopcount_limit
              Limit the number of Received: message headers.

       notify_classes
              List of error classes. Of special interest are:

              policy When  a  client  violates any policy, mail a
                     transcript of the entire SMTP session to the
                     postmaster.

              protocol
                     When  a client violates the SMTP protocol or
                     issues  an  unimplemented  command,  mail  a
                     transcript of the entire SMTP session to the
                     postmaster.

       smtpd_banner
              Text that follows the 220 status code in  the  SMTP
              greeting banner.

       smtpd_expansion_filter
              Controls  what  characters  are  allowed  in  $name
              expansion of rbl template responses and other text.

       smtpd_recipient_limit
              Restrict  the  number  of  recipients that the SMTP
              server accepts per message delivery.

       smtpd_timeout
              Limit the time to send a  server  response  and  to
              receive a client request.

       soft_bounce
              Change  hard (5xx) reject responses into soft (4xx)
              reject responses.  This can be useful  for  testing
              purposes.

       verp_delimiter_filter
              The  characters that Postfix accepts as VERP delim-
              iter characters.

Known versus unknown recipients
       show_user_unknown_table_name
              Whether or not to reveal  the  table  name  in  the
              "User  unknown"  responses.  The extra detail makes
              trouble shooting easier but also  reveals  informa-
              tion that is nobody elses business.

       unknown_local_recipient_reject_code
              The response code when a client specifies a recipi-
              ent  whose   domain   matches   $mydestination   or
              $inet_interfaces,  while  $local_recipient_maps  is
              non-empty and does not list the  recipient  address
              or address local-part.

       unknown_relay_recipient_reject_code
              The response code when a client specifies a recipi-
              ent  whose  domain  matches  $relay_domains,  while
              $relay_recipient_maps  is  non-empty  and  does not
              list the recipient address.

       unknown_virtual_alias_reject_code
              The response code when a client specifies a recipi-
              ent  whose  domain  matches $virtual_alias_domains,
              while  the  recipient  is  not  listed   in   $vir-
              tual_alias_maps.

       unknown_virtual_mailbox_reject_code
              The response code when a client specifies a recipi-
              ent whose domain matches  $virtual_mailbox_domains,
              while the recipient is not listed in $virtual_mail-
              box_maps.

Resource controls
       line_length_limit
              Limit the amount of memory in bytes  used  for  the
              handling of partial input lines.

       message_size_limit
              Limit the total size in bytes of a message, includ-
              ing on-disk storage for envelope information.

       queue_minfree
              Minimal amount of free space in bytes in the  queue
              file  system for the SMTP server to accept any mail
              at all.

       smtpd_history_flush_threshold
              Flush  the  command  history  to  postmaster  after
              receipt of RSET etc.  only if the number of history
              lines exceeds the given threshold.

Tarpitting
       smtpd_error_sleep_time
              Time to wait in seconds before sending a 4xx or 5xx
              server error response.

       smtpd_soft_error_limit
              When an SMTP client has made this number of errors,
              wait error_count seconds before responding  to  any
              client request.

       smtpd_hard_error_limit
              Disconnect  after  a client has made this number of
              errors.

       smtpd_junk_command_limit
              Limit the number of times a client can issue a junk
              command  such  as  NOOP,  VRFY, ETRN or RSET in one
              SMTP session before it  is  penalized  with  tarpit
              delays.

Delegated policy
       smtpd_policy_service_timeout
              Time  limit  for  connecting  to,  writing  to  and
              receiving from a delegated SMTPD policy server.

       smtpd_policy_service_max_idle
              Time after which an  unused  SMTPD  policy  service
              connection is closed.

       smtpd_policy_service_timeout
              Time  after  which  an  active SMTPD policy service
              connection is closed.

UCE control restrictions
       parent_domain_matches_subdomains
              List of Postfix features that use  domain.tld  pat-
              terns   to  match  sub.domain.tld  (as  opposed  to
              requiring .domain.tld patterns).

       smtpd_client_restrictions
              Restrict what clients may connect to this mail sys-
              tem.

       smtpd_helo_required
              Require  that  clients  introduce themselves at the
              beginning of an SMTP session.

       smtpd_helo_restrictions
              Restrict what client hostnames are allowed in  HELO
              and EHLO commands.

       smtpd_sender_restrictions
              Restrict  what sender addresses are allowed in MAIL
              FROM commands.

       smtpd_recipient_restrictions
              Restrict what recipient addresses  are  allowed  in
              RCPT TO commands.

       smtpd_etrn_restrictions
              Restrict what domain names can be used in ETRN com-
              mands, and what clients may issue ETRN commands.

       smtpd_data_restrictions
              Restrictions on the DATA  command.  Currently,  the
              only   restriction   that   makes   sense  here  is
              reject_unauth_pipelining.

       allow_untrusted_routing
              Allow untrusted clients to specify  addresses  with
              sender-specified  routing.   Enabling this opens up
              nasty relay loopholes involving trusted  backup  MX
              hosts.

       smtpd_restriction_classes
              Declares  the  name of zero or more parameters that
              contain a list of UCE restrictions.  The  names  of
              these  parameters  can  then be used instead of the
              restriction lists that they represent.

       smtpd_null_access_lookup_key
              The lookup key to be used in  SMTPD  access  tables
              instead  of  the null sender address. A null sender
              address cannot be looked up.

       maps_rbl_domains (deprecated)
              List of DNS domains that publish the  addresses  of
              blacklisted hosts. This is used with the deprecated
              reject_maps_rbl restriction.

       permit_mx_backup_networks
              Only domains  whose  primary  MX  hosts  match  the
              listed   networks   are   eligible   for  the  per-
              mit_mx_backup feature.

       relay_domains
              Restrict what domains this mail system  will  relay
              mail  to.  The  domains  are routed to the delivery
              agent specified with the relay_transport setting.

Sender/recipient address verification
       Address verification is implemented by sending probe email
       messages  that  are not actually delivered, and is enabled
       via   the   reject_unverified_{sender,recipient}    access
       restriction.   The  status of verification probes is main-
       tained by the address verification service.

       address_verify_poll_count
              How many times to query  the  address  verification
              service  for  completion of an address verification
              request.  Specify 1 to implement a simple  form  of
              greylisting,  that is, always defer the request for
              a new sender or recipient address.

       address_verify_poll_delay
              Time to wait after querying the  address  verifica-
              tion service for completion of an address verifica-
              tion request.

UCE control responses
       access_map_reject_code
              Response code when  a  client  violates  an  access
              database restriction.

       default_rbl_reply
              Default template reply when a request is RBL black-
              listed.  This template is used by the  reject_rbl_*
              and    reject_rhsbl_*   restrictions.   See   also:
              rbl_reply_maps and smtpd_expansion_filter.

       defer_code
              Response code when a client request is rejected  by
              the defer restriction.

       invalid_hostname_reject_code
              Response   code   when   a   client   violates  the
              reject_invalid_hostname restriction.

       maps_rbl_reject_code
              Response code when a request is RBL blacklisted.

       multi_recipient_bounce_reject_code
              Response code  when  a  multi-recipient  bounce  is
              blocked.

       rbl_reply_maps
              Table  with  template responses for RBL blacklisted
              requests, indexed by RBL domain  name.  These  tem-
              plates   are   used   by   the   reject_rbl_*   and
              reject_rhsbl_*     restrictions.     See      also:
              default_rbl_reply and smtpd_expansion_filter.

       reject_code
              Response  code  when  the  client  matches a reject
              restriction.

       relay_domains_reject_code
              Response code when a client attempts to violate the
              mail relay policy.

       unknown_address_reject_code
              Response   code   when   a   client   violates  the
              reject_unknown_address restriction.

       unknown_client_reject_code
              Response code when a client without address to name
              mapping violates the reject_unknown_client restric-
              tion.

       unknown_hostname_reject_code
              Response  code   when   a   client   violates   the
              reject_unknown_hostname restriction.

       unverified_sender_reject_code
              Response  code when a sender address is known to be
              undeliverable.

       unverified_recipient_reject_code
              Response code when a recipient address is known  to
              be undeliverable.

SEE ALSO
       cleanup(8) message canonicalization
       master(8) process manager
       syslogd(8) system logging
       trivial-rewrite(8) address resolver
       verify(8) address verification service

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

                                                         SMTPD(8)