Enhanced status code

SMTP error X.6.7

Non-ASCII addresses not permitted

Updated Jul 1, 2026

The short answer

Non-ASCII addresses not permitted Common cause: Server / client does not support internationalized mailbox address

Quick fix

Use an ASCII address or SMTPUTF8-capable infrastructure

This code is written X.6.7 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 an ASCII address or SMTPUTF8-capable infrastructure

Related codes

X.6.0 Other or undefined media error X.6.1 Media not supported X.6.2 Conversion required and prohibited X.6.3 Conversion required but unsupported X.6.4 Conversion with loss performed X.6.5 Conversion failed
All SMTP error codes
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