Hello.
The IETF has just published STD 72 (aka RFC6409) "Message Submission for Mail", which obsoletes RFC4409 (same subject) and is now the ultimate reference on message submission processes.
Abstract follows:
This memo splits message submission from message relay, allowing each
service to operate according to its own rules (for security, policy,
etc.), and specifies what actions are to be taken by a submission
server.
Message relay is unaffected, and continues to use SMTP over port 25.
When conforming to this document, message submission uses the
protocol specified here, normally over port 587.
This separation of function offers a number of benefits, including
the ability to apply specific security or policy requirements.
This Internet Standard therefore mandates a strong logical separation between MSA and MTA processes in a mail server, defined this way:
- Message Submission Agent (MSA): An MSA acts as a submission server to accept messages from MUAs, and it either delivers them or acts as an SMTP client to relay them to an MTA.
- Message Transfer Agent (MTA): An MTA acts as an SMTP server to accept messages from an MSA or another MTA, and it either delivers them or acts as an SMTP client to relay them to another MTA.
(MUA is the Message User Agent, ie the user's email client with which the user prepares and submits email messages to the server.)
Now I amaware that Mercury may already accept mail from different ports, but this STD goes further stating that different sets of filtering rules and/or security policies should be applied when the server is acting as an MSA (port 587) or an MTA (port 25), which is a powerful idea to better fight against spam and such.
I am therefore wondering if we can expect a future release of Mercury to be fully compliant with this STD and implement such a feature.
Regards,
Corrado