Enhanced status code

SMTP error X.7.27

Sender address has null MX

Updated Jul 1, 2026

The short answer

Sender address has null MX Common cause: Sender domain explicitly declares it receives no mail

Quick fix

Use a valid return-path domain that accepts mail

This code is written X.7.27 because the reason is the same whether the failure is temporary (a 4 first digit) or permanent (a 5). Read the first digit of your own bounce to know which applies.

How to fix it

Use a valid return-path domain that accepts mail

Related codes

X.7.0 Other or undefined security status X.7.1 Delivery not authorized X.7.2 Mailing list expansion prohibited X.7.3 Security conversion required but impossible X.7.4 Security features not supported X.7.5 Cryptographic failure
All SMTP error codes
Ready when you are

Most rejections come back to sender reputation.

Blocklists, auth failures, and policy blocks are what warmup prevents. Warm up your domain so your mail is trusted before you hit send.

Start 7-day free trial Book a demo
7-day free trialNo credit cardCancel anytime