Enhanced status code

SMTP error X.1.0

Other address status

Updated Jul 1, 2026

The short answer

Other address status Common cause: Unspecified problem with sender or recipient address

Quick fix

Verify the complete email address and domain

This code is written X.1.0 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

Verify the complete email address and domain

Related codes

X.1.1 Bad destination mailbox address X.1.2 Bad destination system address X.1.3 Bad destination mailbox address syntax X.1.4 Destination mailbox address ambiguous X.1.5 Destination address valid X.1.6 Destination mailbox moved, no forwarding address
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.

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