Issue
In the Attachments section, I am seeing an attachment with the error "Unfileable attachment, upload via FYI web" and the attachment is titled "ATP Scan In Progress".
Note: If you are seeing only the error "Unfileable attachment, upload via FYI web" without the reference to "ATP Scan in progress", refer to Filing Attachments that cannot be Auto-filed or Opened.
Cause
This is caused by Microsoft Automatic Threat Protection (ATP) and Dynamic Delivery for Attachments and relates to the ATP security scan that you are using in your practice.
Refer to this article from Microsoft Dynamic Delivery in Safe Attachments policies
When ATP Dynamic Delivery is enabled, it replaces the attachments with a placeholder until it has scanned them and confirmed that they are safe. It then adds them back in. FYI picks the email and attachments as soon as they are delivered so we are picking up the 'ATP Scan In Progress' placeholder rather than the actual attachment that is being held back.
Solution
The message regarding the ATP Scan in Progress is temporary. Wait a few minutes until ATP has finished the scan and you will then be able to file the attachments.
If needed you can file the attachment manually. Refer to Filing Attachments that cannot be Auto-filed or Opened.