Microsoft 365 4.7.5
Remote certificate failed MTA-STS validation
Microsoft 365 4.7.5 means: remote certificate failed MTA-STS validation. It is a temporary failure, so your server retries it. The fix is in the sending or receiving configuration named above, not in the list. Fix that, then resend.
Microsoft 365’s exact wording
Quoted from Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Online, checked 2026-11-05. Placeholders are Microsoft 365’s own.
Provider's description
Remote certificate failed MTA-STS validation. Reason: <validityStatus>
Possible cause
The destination mail server's certificate must chain to a trusted root Certificate Authority and the Common Name or Subject Alternative Name must contain an entry for the host name in the STS policy.
Provider's advice
This error usually indicates an issue with the destination mail server's certificate.
| Who sends it | Microsoft 365, Exchange Online and Outlook.com |
|---|---|
| Basic code | Microsoft 365 lists the enhanced code only |
| Enhanced code | 4.7.5: Cryptographic failure |
| Permanent or temporary | Temporary (4xx) |
| Verifying the list prevents it | No |
What the sender should do
The fix is in the sending or receiving configuration named above, not in the list. Fix that, then resend.
Would verifying the list have prevented Microsoft 365 4.7.5?
No
This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Common questions
- What does Microsoft 365 4.7.5 mean?
- Microsoft 365 4.7.5 means: remote certificate failed MTA-STS validation. It is a temporary failure, so your server retries it. The fix is in the sending or receiving configuration named above, not in the list. Fix that, then resend.
- Should I retry after Microsoft 365 4.7.5?
- Your sending server retries it automatically, because it is a temporary (4xx) failure. Investigate only if it keeps coming back over several hours.
- Would verifying my list have prevented Microsoft 365 4.7.5?
- No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Sources
- Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Online (checked 2026-11-05)
- IANA: SMTP Enhanced Status Codes registry (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05