450 4.1.8 Sender address rejected: Domain not found
Sample bounce line
450 4.1.8 <[email protected]>: Sender address rejected: Domain not found
What it means
The receiving Postfix server rejected the MAIL FROM address because its domain could not be found in DNS. RFC 3463 defines X.1.8 as Bad sender's system address: the sender's system does not exist or cannot accept return mail, meaning the part right of the @ is invalid for mail. The 450 class-4 reply is temporary, so the sender may retry.
Why it happens
- The envelope sender domain does not exist in DNS or has a typo or expired registration
- Locally generated mail (web app, content filter) using a made-up or unresolvable sender address; in the 2012 postfix-users thread the rejected mail came from localhost and the suggested causes were a content filter, proxy filter or web application talking SMTP
- Postfix has reject_unknown_sender_domain in smtpd_sender_restrictions (SMTPD_ACCESS_README: 'Don't accept mail from domains that don't exist')
How to fix it
- Sender: use a real sender address on a domain with working DNS
- Fix or register the sender domain's DNS records
- Postfix admin: correct the sender address of local applications, and check whether virtual domains are configured in virtual_alias_domains rather than mydestination
Check your domain now
Many of these errors come from missing or broken SPF, DKIM, DMARC or reverse DNS records. Enter your domain to run the free check.
Related errors
No related errors listed yet.