What to do
- Give the sending domain real MX records.
How it appears in a bounce
550 5.7.27 Sender address has null MXPaste the full bounce into the decoder — it finds every code and recipient and says what to check.
SMTP 5.7.27 Sender address has null MX
The sender domain says it receives no mail (null MX), so bounces cannot go back.
5.7.27
- Class
- 5xx · Permanent failure
- Retried?
- No, the message bounces
- Defined in
- RFC 7372 / provider