SMTP(8) SMTP(8) NAME smtp - Postfix remote delivery via SMTP SYNOPSIS smtp [generic Postfix daemon options] DESCRIPTION The SMTP client processes message delivery requests from the queue manager. Each request specifies a queue file, a sender address, a domain or host to deliver to, and recip- ient information. This program expects to be run from the master(8) process manager. The SMTP client updates the queue file and marks recipi- ents as finished, or it informs the queue manager that delivery should be tried again at a later time. Delivery problem reports are sent to the bounce(8) or defer(8) dae- mon as appropriate. The SMTP 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 the domain or host is specified as a comma/whitespace separated list, the SMTP client repeats the above process for all destinations until it finds a server that responds. Once the SMTP client has received the server greeting ban- ner, no error will cause it to proceed to the next address on the mail exchanger list. Instead, the message is either bounced, or its delivery is deferred until later. SECURITY The SMTP client is moderately security-sensitive. It talks to SMTP servers and to DNS servers on the network. The SMTP 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 2045 (MIME: Format of Internet Message Bodies) RFC 2046 (MIME: Media Types) RFC 2554 (AUTH command) RFC 2821 (SMTP protocol) RFC 2920 (SMTP Pipelining) DIAGNOSTICS Problems and transactions are logged to syslogd(8). Cor- rupted 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 postmaster is notified of bounces, protocol problems, and of other trouble. BUGS 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. Miscellaneous best_mx_transport Name of the delivery transport to use when the local machine is the most-preferred mail exchanger (by default, a mailer loop is reported, and the message is bounced). debug_peer_level Verbose logging level increment for hosts that match 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. disable_dns_lookups Disable DNS lookups. This means that mail must be forwarded via a smart relay host. error_notice_recipient Recipient of protocol/policy/resource/software error notices. fallback_relay Hosts to hand off mail to if a message destination is not found or if a destination is unreachable. ignore_mx_lookup_error When a name server fails to respond to an MX query, search for an A record instead deferring mail delivery. inet_interfaces The network interface addresses that this mail sys- tem receives mail on. When any of those addresses appears in the list of mail exchangers for a remote destination, the list is truncated to avoid mail delivery loops. See also the proxy_interfaces parameter. notify_classes When this parameter includes the protocol class, send mail to the postmaster with transcripts of SMTP sessions with protocol errors. proxy_interfaces Network interfaces that this mail system receives mail on by way of a proxy or network address trans- lator. When any of those addresses appears in the list of mail exchangers for a remote destination, the list is truncated to avoid mail delivery loops. See also the inet_interfaces parameter. smtp_always_send_ehlo Always send EHLO at the start of a connection. smtp_never_send_ehlo Never send EHLO at the start of a connection. smtp_bind_address Numerical source network address to bind to when making a connection. smtp_line_length_limit Length limit for SMTP message content lines. Zero means no limit. Some SMTP servers misbehave on long lines. smtp_helo_name The hostname to be used in HELO and EHLO commands. smtp_skip_4xx_greeting Skip servers that greet us with a 4xx status code. smtp_skip_5xx_greeting Skip servers that greet us with a 5xx status code. smtp_skip_quit_response Do not wait for the server response after sending QUIT. smtp_pix_workaround_delay_time The time to pause before sending .<CR><LF>, while working around the CISCO PIX firewall <CR><LF>.<CR><LF> bug. smtp_pix_workaround_threshold_time The time a message must be queued before the CISCO PIX firewall <CR><LF>.<CR><LF> bug workaround is turned on. MIME Conversion disable_mime_output_conversion Disable the conversion of 8BITMIME format to 7BIT format when the remote system does not advertise 8BITMIME support. mime_boundary_length_limit The amount of space that will be allocated for MIME multipart boundary strings. The MIME processor is unable to distinguish between boundary strings that do not differ in the first $mime_bound- ary_length_limit characters. mime_nesting_limit The maximal nesting level of multipart mail that the MIME processor can handle. Refuse mail that is nested deeper, when converting from 8BITMIME format to 7BIT format. Authentication controls smtp_sasl_auth_enable Enable per-session authentication as per RFC 2554 (SASL). By default, Postfix is built without SASL support. smtp_sasl_password_maps Lookup tables with per-host or domain name:password entries. No entry for a host means no attempt to authenticate. smtp_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. Resource controls smtp_destination_concurrency_limit Limit the number of parallel deliveries to the same destination. The default limit is taken from the default_destination_concurrency_limit parameter. smtp_destination_recipient_limit Limit the number of recipients per message deliv- ery. The default limit is taken from the default_destination_recipient_limit parameter. Timeout controls The default time unit is seconds; an explicit time unit can be specified by appending a one-letter suffix to the value: s (seconds), m (minutes), h (hours), d (days) or w (weeks). smtp_connect_timeout Timeout for completing a TCP connection. When no connection can be made within the deadline, the SMTP client tries the next address on the mail exchanger list. smtp_helo_timeout Timeout for receiving the SMTP greeting banner. When the server drops the connection without send- ing a greeting banner, or when it sends no greeting banner within the deadline, the SMTP client tries the next address on the mail exchanger list. smtp_helo_timeout Timeout for sending the HELO command, and for receiving the server response. smtp_mail_timeout Timeout for sending the MAIL FROM command, and for receiving the server response. smtp_rcpt_timeout Timeout for sending the RCPT TO command, and for receiving the server response. smtp_data_init_timeout Timeout for sending the DATA command, and for receiving the server response. smtp_data_xfer_timeout Timeout for sending the message content. smtp_data_done_timeout Timeout for sending the "." command, and for receiving the server response. When no response is received, a warning is logged that the mail may be delivered multiple times. smtp_quit_timeout Timeout for sending the QUIT command, and for receiving the server response. SEE ALSO bounce(8) non-delivery status reports master(8) process manager qmgr(8) queue 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 Yorktown Heights, NY 10598, USA SMTP(8)