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~/errors / SMTP / Mail

Postfix: mail for example.com loops back to myself

Postfix looked up where to send the mail and ended up at itself, so it stops instead of looping forever. The routing says this host is responsible, but the local configuration does not accept the domain.

daniele@mikweb: ~/errors — less postfix-mail-for-domain-loops-back-to-myself.md

What the message looks like

postfix/smtp[1822]: 7B2C14A0F3: to=<info@example.com>, relay=none, delay=0.1, status=bounced (mail for example.com loops back to myself)

Common causes

  • The MX record of the domain points to this server, but the domain is not in mydestination or virtual_mailbox_domains.
  • A relayhost or a transport entry sends the domain to a host name that resolves to this same machine.
  • The MX host name or the relayhost resolves to an address of this server, for example after a move or a changed DNS record.
  • The domain sits in both mydestination and a virtual domain list, or myhostname differs from the name in the MX.

Check

  1. What are the MX records of the domain?
    dig +short MX example.com
  2. What do the MX hosts resolve to?
    dig +short A mail.example.com
  3. Which addresses does this server have?
    ip -brief address
  4. Routing and domain settings
    postconf -n | grep -E 'myhostname|mydestination|relayhost|virtual_mailbox_domains|transport_maps'

Fix

  • If this server should receive mail for the domain, add the domain to virtual_mailbox_domains (or to mydestination), but to one list only, and define where the mailboxes are.
  • If another server should receive it, correct the MX record to point there, and remove the entry in transport_maps or the relayhost that points back to this machine.
  • Make myhostname match the real host name, and check that no name in the routing resolves to your own IP unless intended.
  • Apply with postfix reload, then retry the stuck messages with postqueue -f.
  • Send a test mail and watch journalctl -u postfix to see the delivery.

FAQ

What is the difference to a hop count exceeded bounce?

Hop count exceeded (554 5.4.14) appears after a mail has travelled around a loop between servers. Loops back to myself is caught earlier, on the first lookup.

Does a backup MX cause this?

It can. A secondary MX that you list for a domain must be set up as a relay for it (relay_domains with a transport), or it will refuse or loop the mail.

daniele@mikweb: ~/blog — ls

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daniele@mikweb: ~/errors — ls

More errors

550 5.4.1 Recipient address rejected: Access deniedSMTP: 550 5.4.1 Recipient address rejected: Access denied550 5.7.1SMTP 550 5.7.1: relay access denied and policy rejections550 5.7.26SMTP 550 5.7.26 and 5.7.23: unauthenticated email421 4.7.0SMTP 421 4.7.0: temporarily rate limited, try again later450 4.1.8 Sender address rejected: Domain not foundSMTP: 450 4.1.8 Sender address rejected: Domain not found554 5.7.1 Relay access deniedSMTP: 554 5.7.1 Relay access denied

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