Analyzing Exchange Message Delete Events in the Office 365 Audit Log

Exchange Online writes audit records into the Office 365 audit log when messages are deleted by delegates and administrative action. We can analyze the audit records to find out who deleted a specific message. Some challenges exist to interpret the audit records for admin-generated deletions (for example, when you run Search-Mailbox), but it’s easy enough to code the necessary checks in PowerShell.

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What’s Happening with the MailItemsAccessed Audit Event

Microsoft launched the MailItemsAccessed audit event (to capture when email is opened) in January, reversed the roll-out in April, and now might restart sometime in Q3. It’s an odd situation that isn’t really explained by a statement from Microsoft. Are they going to charge extra for this audit event? Will they be analyzing the events? Or does Office 365 capture too many mail items accessed events daily?

The Sad Case of Truncated Office 365 Audit Events

On May 7, Microsoft eventually fixed a truncation bug that affected group events (creation, add member, etc.) ingested into the Office 365 audit log. The fix took far too long coming and the overall response is certainly not Microsoft’s finest hour. Audit events, after all, are pretty important in compliance scenarios and it’s not good when those events are incomplete.

Microsoft Halts Deployment of MailItemsAccessed Audit Records

Announced in January, paused in March – that’s the fate of the MailItemsAccessed audit record generated by Exchange Online for the Office 365 audit log. Microsoft found some problems that they are fixing, which is good (because you want audit data to be reliable). And when the fixes are available, the deployment of the new audit record will restart.

Office 365 Captures Audit Records for Teams Compliance Items

Office 365 Audit Log Search

In one of those interesting (but possibly worthless) facts discovered about Office 365, we find that audit records are captured for Teams compliance records written into Exchange Online group mailboxes. The Search-UnifiedAuditLog cmdlet reveals details that we can interpret using some techniques explained in Chapter 21 of the Office 365 for IT Pros eBook.