Email error codes and bounce messages, explained

A bounce message is the receiving server telling you why a message was not delivered. Find your code below to see what it means, whether the address is bad or your setup is, and what to do next.

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Permanent errors: the address or domain is not valid

550 5.1.1User unknown (mailbox does not exist) 550 5.4.1Recipient address rejected: access denied 553 5.1.3Invalid address syntax 550 5.2.1Mailbox disabled or not accepting mail 550 5.1.2Bad destination domain (domain not found)

Temporary errors: try again later

552 5.2.2Mailbox full (over quota) 421 4.7.0Try again later (rate limited or temporarily deferred) 450 4.2.1Mailbox temporarily unavailable 451 4.7.1Greylisted: try again later 452 4.2.2Insufficient storage or too many recipients 421 4.4.1Connection timed out

Sender and policy errors: fix your setup

550 5.7.1Message rejected by policy (blocked) 550 5.7.26Sender not authenticated (SPF/DKIM/DMARC) 554 5.7.1Transaction failed: service unavailable or blocked 535 5.7.8Authentication failed (SMTP login) Spam rejectionMessage flagged as spam

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