Attachments aren't tracked to Microsoft Dynamics 365 after Microsoft Defender for Office 365 is enabled
Applies to: Microsoft Dynamics 365 Customer Engagement Online
Original KB number: 4522769
When you use server-side synchronization with Microsoft Dynamics 365 and Microsoft Defender for Office 365 is enabled, attachments may be missing from the email created in Microsoft Dynamics 365. You may see an attachment included named ATP Scan in Progress.eml, but the original attachment isn't added to Microsoft Dynamics 365.
If a Safe Attachments policy in Microsoft Defender for Office 365 is configured with the Dynamic Delivery action, and an email is received in the user's inbox with an attachment, two emails with the same email message ID will exist. The user will receive the first one without the original attachment while Safe Attachments is scanning the attachments. The second email will replace the first one after the scanning completes.
The server-side synchronization feature will only track emails with the same message ID once to avoid duplication. If the second email doesn't get to Exchange before the sync cycle starts from Microsoft Dynamics 365, the original attachment may not be tracked to the system.
To solve the issue, use a different action (for example, the Block action) in the Safe Attachments policy.
For more information, see Safe Attachments policy settings in Microsoft Defender for Office 365.