Microsoft 365 5.0.350
Generic error, x-dg-ref header is too long, or Requested action not taken: policy violation detected (AS345)
Microsoft 365 5.0.350 means: generic error, x-dg-ref header is too long, or Requested action not taken: policy violation detected (AS345). It is a permanent failure, so do not retry it unchanged. 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
Generic error, x-dg-ref header is too long, or Requested action not taken: policy violation detected (AS345)
Possible cause
5.0.350 is a generic catch-all error code for a wide variety of nonspecific errors from the recipient's email organization. The specific x-dg-ref header is too long message is related to Rich Text-formatted messages. The specific Requested action not taken: policy violation detected (AS345) message is related to nested attachments.
| Who sends it | Microsoft 365, Exchange Online and Outlook.com |
|---|---|
| Basic code | Microsoft 365 lists the enhanced code only |
| Enhanced code | 5.0.350: Microsoft 365-specific, not in the IANA registry. Its subject digit puts it under 5.0.0 other undefined status. |
| Permanent or temporary | Permanent (5xx) |
| 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 5.0.350?
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 5.0.350 mean?
- Microsoft 365 5.0.350 means: generic error, x-dg-ref header is too long, or Requested action not taken: policy violation detected (AS345). It is a permanent failure, so do not retry it unchanged. 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 5.0.350?
- No. It is a permanent (5xx) failure, so the same message to the same address will fail again. Fix the cause first. The fix is in the sending or receiving configuration named above, not in the list. Fix that, then resend.
- Would verifying my list have prevented Microsoft 365 5.0.350?
- 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)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05