smtp.rfc2142.postmaster

postmaster@ Not Accepting Mail

What we check

We send a RCPT TO:<postmaster@domain> command during the SMTP session to verify that the server accepts mail for the postmaster role address. RFC 5321 requires every SMTP server to accept mail for postmaster@ — it is the mandatory administrative contact for the mail system.

What this finding means

The server rejected RCPT TO:<postmaster@domain>. The postmaster address is either not configured, aliased to a non-existent mailbox, or explicitly blocked by recipient restrictions.

Why it matters

RFC violation. RFC 5321 §4.5.1 states: "every SMTP server MUST accept mail directed to the mailbox defined by the local part 'postmaster'." This is not optional guidance — it is a protocol requirement.
Unreachable for error reports. Other mail server operators send delivery problems, abuse reports, and configuration errors to postmaster@. If the address bounces, you miss critical operational signals.
Trust signal. Rejecting a mandatory address suggests the mail system is misconfigured or unmaintained, which affects how other operators perceive the domain.

How to fix

Create the postmaster alias. For Postfix:

# /etc/postfix/virtual or /etc/aliases
postmaster@example.com  admin@example.com

Then rebuild the alias database:

postalias /etc/postfix/aliases   # or: postmap /etc/postfix/virtual
postfix reload

Check recipient restrictions. Ensure smtpd_recipient_restrictions does not reject postmaster before permit:
```
smtpd_recipient_restrictions =
    permit_mynetworks,
    reject_unauth_destination,
    check_recipient_access hash:/etc/postfix/recipient_access
```
In recipient_access, do not list postmaster@ with a REJECT action.
For hosted mail (Microsoft 365, Google Workspace): ensure the postmaster alias is configured in your admin console. Most hosted platforms accept postmaster@ by default, but custom routing rules can break it.

How it's graded

A rejected postmaster address carries a 15-point penalty in the MX category. See Grading Methodology for the full scoring model.

Evidence example

C: RCPT TO:<postmaster@example.com>
S: 550 5.1.1 <postmaster@example.com>: Recipient address rejected: User unknown