Generic SMTP
553 5.1.2 — the recipient's domain can't be found
553 5.1.2
In the enhanced status codes standard, X.1.2 means a bad destination system address: the part of the address after the @ doesn't lead to a mail system. Gmail returns it as 553 5.1.2 "We weren't able to find the recipient domain. Please check for any spelling errors". Other servers phrase it differently, but the meaning is the same: the domain doesn't exist, or DNS doesn't say where its mail should go.
How to fix it
- 1
Check the domain for typos
The most common cause is a misspelled domain: gmial.com, outlok.com, a missing letter in a company name, or .con instead of .com. Compare the address against a recent email from that person.
- 2
Look up the domain's MX records
Run the MX lookup on the recipient domain. No MX and no address record means mail has nowhere to go. A "null MX" (a single MX record of priority 0 pointing at ".") means the domain explicitly accepts no email.
- 3
If it's your own domain
Senders get 5.1.2 for your domain when its MX records disappeared, for example after moving DNS hosting without copying the mail records, or when the domain registration lapsed. Restore the MX records from your mail provider's setup instructions and confirm the domain is renewed.
- 4
If the domain should exist
Check that the domain is registered and its nameservers answer. An expired domain or a broken nameserver delegation looks the same as a domain that doesn't exist.
Meaning current as of 2026-10-24, cross-checked against the provider's own documentation. Providers do occasionally redefine codes — if this doesn't match what you're seeing, the source link is the authoritative reference.