SMTP codes
SMTP 4.4.1 No answer from host
The receiving server did not answer: down, or port 25 blocked on the way. Your server keeps retrying.
- Class
- 4xx · Temporary failure
- Retried?
- Yes, the sending server retries
- Defined in
- RFC 3463
What to do
- Check the recipient domain’s MX and that port 25 to it is open from your server.
- Many cloud providers block outgoing port 25 by default.
How it appears in a bounce
450 4.4.1 No answer from host
Paste the full bounce into the decoder — it finds every code and recipient and says what to check.