The submission service is used by local users to send mails to either other local users, or to other domains on the internet. The service, in turn, transmits mails to the public SMTP server of the recipient domain, delivers them locally, relays them locally, etc. This service is specified by RFC 4409, Message Submission for Mail. It is a variant of SMTP.
If the transmission of a mail to a remote domain fails on the first attempt, then it retries the transmission several times. If it eventually decides that the mail is undeliverable, then it sends a delivery status notification message back to the sender.
A dedicated MSA is useful for people, who are working outside of the office, and whose internet service provider blocks port 25. The service usually runs on port 587. Its address is NOT published in a DNS MX record.
Configuration files specific to the Message Submission service are located in the
|The primary configuration file of the Submission
service. It configures the SMTP server, the filter chain, and most
filter parameters. In turn, it imports all the other configuration files of
the Submission service.
|List of ip addresses or address ranges.
Mails can be submitted from these ip addresses without any further authentication.
This file is imported by
|The submission service uses file system based
queues to make sure no mails are lost. Until a mail is confirmed to be received
by the recipient domain the mail stays in a queue. The queues are managed by
In the default configuration there are three transmitters and there are
three correspongind queues.