Bounce and error codes

Pick the shelf that matches what you are holding, then the code.

Last updated 20 Sep 2026

Not sure which kind you have? Hard bounce vs soft bounce sorts every code by who owns the fix.

A bounce, and no code yet

The words at the top of the notice, and where the real reason sits under them.

Mail Delivery Subsystem did your message arrive? Message blocked read Gmail's bounce and fix the cause Delivery Status Notification Failure what to do next Email bounced back read the reason line and fix it Your message could not be delivered fix the Outlook NDR 550 permanent failure what it means and how to clear it Message not delivered what Gmail's bounce means, and the fix Undelivered Mail Returned to Sender read the Postfix bounce

SPF, DKIM or DMARC failed

The address is fine. The receiver checked your domain's DNS and refused. These are yours to fix.

550 5.7.515 why Outlook rejects your mail, and the fix 550 5.7.509 does not pass DMARC verification, fixed 550 5.7.26 Gmail blocked your unauthenticated email 550 5.7.1 rejected per DMARC policy causes and fix 550 5.7.23 SPF validation failed at Microsoft 365 dmarc=fail (p=REJECT) reading the header, and the fix SPF PermError too many DNS lookups, and how to fix it DKIM body hash did not verify what changed your mail

The address or the mailbox

No DNS change clears these. The fix is the address you typed, or an admin at the other end.

550 5.4.1 Recipient address rejected who can clear it 550 5.1.1 the mailbox does not exist, and the fix 550 5.2.1 the mailbox exists and is not accepting mail

Spam, reputation or a rule at the recipient

Authentication passed and the receiver still refused. Slower to clear, and still on your side.

421 4.7.28 Gmail is rate limiting your IP or domain 554 5.7.1 which rejection you have, and the fix 550 5.7.350 the remote server refused the message 550 5.7.520 the tenant blocked external forwarding

No bounce at all

The receiver accepted the message and held it. Your DMARC reports are the only view of that.

Email quarantined no bounce, and what a sender fixes Email delivery failed with no bounce where it went and why

Elsewhere on the site

SPF and DKIM by provider The records each platform needs, and where alignment breaks. Guides Setup, alignment, aggregate reports and the ten-lookup limit.

Or check a domain right now with the free DMARC, SPF and DKIM lookups.

See the bounce before your customer does

A rejection is the last warning, not the first. The reports name the failing sender days before its volume is high enough to bounce. On a paid plan, that first failing report becomes an email the same day. One summary a week, and your first domain is free.

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