Troubleshooting Missing Emails After a Microsoft 365 / Exchange Migration

This article provides a troubleshooting checklist for the most common reasons why emails may appear to be missing after a migration from Microsoft Exchange or Microsoft 365. By default, CloudM Migrate is designed to migrate all standard email, so if users report missing items, it is typically due to one of the following scenarios.

1. Check the Item Type (Message Class)

This is the most common reason for items being skipped. By default, CloudM Migrate is configured to migrate standard, user-generated emails and will skip other item types like Non-Delivery Reports (NDRs), read receipts, or system messages.

• Cause: CloudM Migrate defaults to migrating only items with the message class IPM.Note and its subclasses. Items with different classes (e.g., IPM.Report.*) are intentionally skipped and will not be logged as failures.

• How to Investigate: If you need to migrate non-standard email types, you can expand the scope.

• Solution (If Required):

  1. Navigate to Configuration > Source Settings > Email.

  2. In the Included Item Classes field, you can add other message classes.

  Warning: Adding other classes is an unsupported configuration. These item types may have conversion issues that CloudM cannot resolve. For more information on item classes, see the Microsoft Documentation.

2. Check for Duplicates in Multiple Folders

CloudM Migrate includes logic to prevent duplicate items from appearing in the destination mailbox.

• Cause: If a user has the exact same email stored in multiple source folders (e.g., once in the Inbox and a copy in a "Project X" folder), the tool will only migrate the first copy it finds. All subsequent copies will be skipped and logged internally as "Already Exists."

• Impact: This can result in some destination folders being empty or containing fewer items than the source, which is expected behavior. There is no solution or setting to change this, as it protects against data duplication.

3. Check Litigation Hold / Recoverable Items

Emails placed in Litigation Hold or found in the "Recoverable Items" folder are not part of the standard mailbox and are not migrated by default.

• Cause: These items are stored in a non-IPM folder invisible to the user and standard email clients.

• How to Investigate: You can check if a source user has Litigation Hold enabled by running the following PowerShell command against your source Microsoft 365 tenant:

  Get-Mailbox "username" | Format-Table LitigationHold*
  

• Solution: To migrate these items, enable the Include Recoverable Mail Items setting in your batch configuration under the Source Settings.

4. Check the Exchange Online Archive

A user's Online Archive is a separate mailbox from their primary mailbox and must be migrated separately.

• Cause: Data stored in the Exchange Online Archive is not included in a standard primary mailbox migration.

• Solution: You must configure a separate migration for the user's archive. 

5. Check Destination Retention Policies

A policy in the destination environment may be acting on items as soon as they are migrated.

• Cause: If the destination tenant has a strict retention policy, newly migrated emails might be moved to an archive or compliance folder immediately after migration, making them appear "missing" from the user's primary mailbox view.

• Solution: Check the user's Online Archive and other retention folders in the destination. We recommend reviewing and temporarily disabling aggressive retention policies on the destination during the migration period.

6. Review Third-Party Archiving Solutions

External archiving systems can interfere with the migration process.

• Cause: A third-party solution may intercept or immediately archive emails from the source, preventing the migration tool from accessing them.

• Solution: We strongly recommend disabling any third-party email archiving solutions on the source platform before and during the migration.