Microsoft (Outlook.com and Microsoft 365) · permanent error
550 5.0.350 [AS345]: attachment with too many embedded files
The message was rejected because an attachment contains 20 or more embedded files, which is treated as a policy violation.
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- Permanent (5xx)
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At a glance
- Code
- 550 5.0.350 [AS345]
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 5.0.350 Requested action not taken: policy violation detected (AS345)
What it means
Microsoft documents this variant of 550 5.0.350 for nested content: an attachment, such as a Word document, with 20 or more files embedded in it, such as other Word or Excel files. The message is flagged as a policy violation, with the reference AS345, and refused as a whole. Nothing is wrong with the addresses or the sender's reputation; the message goes through once the attachment carries fewer embedded files.
Common causes
- A document attached to the message embeds 20 or more other files.
- Files were inserted into the document as embedded objects rather than attached separately.
How to fix it
- 01Remove some of the embedded files from the attached document and send it again.
- 02Attach the files separately, or share them through a link instead.
- 03If the error persists with fewer embedded files, forward the report to your admin.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Fix NDR error "550 5.0.350" in Exchange Onlinelearn.microsoft.com
- Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
Related codes
Further reading
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