Why was my email rejected?
A bounce tells you a code and almost nothing else. These pages say what the receiving server actually checked before it refused the message, which of SPF, DKIM or DMARC produced the answer, and the record that resolves it.
- 550 5.7.26Gmail
Gmail returned 550 5.7.26 and refused the message. It means neither SPF nor DKIM passed for the domain in your From address. Here is how to find which one failed and the exact DNS record that fixes it.
- 550 5.7.509Microsoft (Outlook.com, Exchange Online)
Microsoft returned 550 5.7.509 because your own DMARC policy told it to reject the message. The policy is working; something legitimate is failing alignment. Here is how to find what.
- 550 5.7.23Microsoft (Exchange Online) and other receivers
A receiving server checked your SPF record, decided the sending server was not allowed, and rejected the message. Here is how to find which server it objected to and publish the record that permits it.
- Authentication-Resultsevery major receiver
The Authentication-Results header records exactly what the receiving server concluded about your mail. It is the fastest way to find out why a message was rejected or filtered — this explains every value you will see in it.
Or just check the domain
Most of these codes come down to one of four things, and a scan finds all four in about two seconds.