📧 Email / SMTP errors

SMTP bounce codes (550, 554, 5.7.x), SPF/DKIM/DMARC rejections and mail delivery errors explained.

CodeErrorWhat it means
550 5.1.1 550 5.1.1 The email account that you tried to reach does not exist (User unknown) The recipient mailbox doesn’t exist on the receiving server — a typo in the address, a deleted account, or a…
550 5.7.1 550 5.7.1 Relaying denied / Message rejected as spam / Unauthenticated email not accepted The receiving (or your outgoing) mail server refused the message — relaying isn’t allowed, the sender isn’t a…
550 5.7.26 550 5.7.26 This mail has been blocked because the sender is unauthenticated (SPF/DKIM/DMARC) Gmail/Outlook rejected the message because SPF and DKIM didn’t pass for the sender’s domain (DMARC failure).