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smtpd



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

              overrides built-in command definitions.


Content inspection controls

       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.


Authentication controls

       enable_sasl_authentication
              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

       always_bcc
              Address  to send a copy of each message that enters
              the system.

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

       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
              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.

       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.


SEE ALSO

       trivial-rewrite(8) address resolver
       cleanup(8) message canonicalization
       master(8) process manager
       syslogd(8) system logging


LICENSE

       The  Secure  Mailer  license must be distributed with this
       software.


AUTHOR(S)

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
  
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