SMTP SUBMIT servers

A TCP/IP channel marked with the   channel option will function with respect to message submission as an  SMTP SUBMIT server, as defined in RFC 6409 (Message Submission for  Mail). Port 587 is reserved for SMTP SUBMIT use, so  is  normally set on the channel  that, in the  Dispatcher configuration,  is associated with port 587; see the   option (Unified Configuration). But SMTP SUBMIT service can also be set up on a different or other ports, if desired: any incoming channel marked  with   will operate as an SMTP SUBMIT server. RFC 5068 (Email Submission Operations: Access and Accountability Requirements), also known as BCP 134, encourages sites to support---and  indeed transition to using---SMTP SUBMIT rather than regular SMTP for  initial submission of user messages.

The configuration established when the MTA is installed normally includes an SMTP SUBMIT server in the form of a    channel;  this channel is marked with the   channel option, and the  Dispatcher configuration sets it to listen on port 587. In accord with RFC 5068&#x27;s recommendations, the channel is also marked with    and  , meaning that  users must authenticate to submit messages to this channel and  may use TLS. See Typical TCP/IP channels and servers for an example. (TLS use should be encouraged, but is not outright required in this typical configuration; sites that prefer to  also require TLS use may instead set   .)

Sites should encourage their local users to submit messages to the SMTP SUBMIT server on port 587, rather than to the regular SMTP server on  port 25. But note that this does also imply that users must authenticate and ought to use TLS---some configuration of the  users&#x27; clients may be needed to achieve this.

Extensions to SMTP SUBMIT permit additional functionality for users and user clients: see the   mapping table  and SMTP SUBMIT FUTURERELEASE support.

See also:
 * Typical TCPIP channels and servers
 * submit Option
 * Dispatcher
 * tcp_ports Option
 * maysasl Option
 * maytls Option
 * MMP and IMAP Proxy and POP Proxy and vdomain options
 * BURL_ACCESS mapping table
 * SMTP SUBMIT FUTURERELEASE support
 * TCPIP channels