550 5.7.1 IP Blocked: Causes, Solutions, and How to Fix It
Code550 5.7.1 Bounce typeHard bounce RetryableNo (until resolved) Action neededIdentify block, fixTypical error message 550 5.7.1 IP blockedWhat does 550 5.7.1 IP blocked ...
Standards & Protocols
550 5.7.25 Reverse DNS Failure: Meaning, Causes, and How to Fix It
550 5.7.25 means the receiver could not verify your sending IP reverse DNS. Complete guide to PTR records, forward-confirmed rDNS, and fixes for every hosting provider and MTA.
550 SPF Sender Invalid Envelope Rejected: Causes and Fix
Code550 Bounce typeHard bounce RetryableYes (after fix) Action neededFix SPF recordTypical error message 550 SPF Sender Invalid - envelope rejectedWhat does 550 SPF Sender ...
SMTP Relaying Denied: Complete Fix for Postfix, Exim, and Sendmail
Getting 550 5.7.1 Relaying Denied or 554 5.7.1 Relay Access Denied? Complete fix guide with Postfix, Exim, and Sendmail configuration for outbound relay authentication.
550 Must Issue STARTTLS: Causes, Solutions, and How to Fix It
Code550 Bounce typeHard bounce RetryableYes (after fix) Action neededEnable STARTTLSTypical error message 550 Must issue a STARTTLS command firstWhat does 550 Must issue ...
Blocked by Spamhaus (zen.spamhaus.org): Complete Delisting Guide
Getting 550 5.7.1 or 554 5.7.1 blocked by zen.spamhaus.org? Complete Spamhaus delisting guide covering SBL, XBL, PBL, CBL, CSS, and DBL with removal procedures and prevention.
550 5.2.1 The Email Account Is Inactive: Causes and Fix
Code550 5.2.1 Bounce typeHard bounce RetryableNo Action neededRemove addressTypical error message 550 5.2.1 The email account that you tried to reach is inactive. For more ...
550 5.1.1 User Unknown: Meaning, Causes, and How to Fix It
550 5.1.1 means the recipient address does not exist on the receiving server. Complete guide to diagnosing typos, deactivated accounts, spam traps, and list hygiene.
550 No Such User: Causes, Solutions, and How to Fix It
Code550 Bounce typeHard bounce RetryableNo Action neededRemove addressTypical error message 550 No such userWhat does 550 No such user mean?The receiving server has ...
454 4.7.1 Relay Access Denied: Causes, Solutions, and How to Fix It
Code454 4.7.1 Bounce typeSoft bounce RetryableYes (after fix) Action neededFix relay authTypical error message 454 4.7.1 Relay access deniedWhat does 454 4.7.1 Relay access ...
452 4.2.2 The Recipient’s Inbox Is Out of Storage Space: Causes and Fix
Code452 4.2.2 Bounce typeSoft bounce RetryableYes (limited) Action neededRetry, then suppressTypical error message 452 4.2.2 The recipient's inbox is out of storage space. Please ...
451 Relay Not Permitted: Causes, Solutions, and How to Fix It
Code451 Bounce typeSoft bounce RetryableYes (after fix) Action neededFix relay configTypical error message 451 relay not permitted!What does 451 relay not permitted mean?The ...
