6. Optional Actions

The MSA MAY do any of the following:

6.1. Enforce Submission Rights

The MSA MAY issue an error response to a MAIL command if the address in MAIL FROM appears to have insufficient submission rights, or is not authorized with the authentication used (if the session has been authenticated).

Reply code 550 with an appropriate enhanced status code per [SMTP-CODES], such as 5.7.1, is used for this purpose.

6.2. Enforce Permissions

The MSA MAY issue an error response to a RCPT command if inconsistent with the permissions given to the user (if the session has been authenticated).

Reply code 550 with an appropriate enhanced status code per [SMTP-CODES], such as 5.7.1, is used for this purpose.

6.3. Check Message Data

The MSA MAY issue an error response to the DATA command or send a failure result after end-of-data if the submitted message is syntactically invalid, or seems inconsistent with permissions given to the user (if known), or violates site policy in some way.

Reply code 554 is used for syntactic problems in the data. Reply code 501 is used if the command itself is not syntactically valid. Reply code 550 with an appropriate enhanced status code per [SMTP-CODES] (such as 5.7.1) is used to reject based on the submitting user. Reply code 550 with an appropriate enhanced status code (such as 5.7.0) is used if the message violates site policy.

6.4. Support for the Postmaster Address

If appropriate under local conditions and to facilitate conformance with the "postmaster" requirements of [SMTP-MTA], the MSA MAY permit a reduced degree of authentication for mail addressed to the "postmaster" (or one of its alternate spelling forms, see [SMTP-MTA]), in one or more domains, as compared to requirements enforced for other addresses. Among other benefits, this provides an address of last resort that can be used by authorized users to report problems that otherwise prevent them from submitting mail.