Problem

During migration to Office 365, you have noticed the following error:
“Failed to write Mail:[Title of your message] ErrorMessageSizeExceeded”

Cause

The mail is larger than EWS allows in the target Office 365.

Resolution

Change the maximum size of message allowed in your target mailbox. You can use following PowerShell scripts:

Step 1. Determine the current user’s settings:

Step 2. Set up new limitations for whole Office 365 tenant:

These limitations will be applied only to new created users. If you have already created your users, use the script from Step 3.

Step 3. Increase limitations for an existing user:

 

To check if modifications are done correctly, run again a command from the Step 1 and restart your migration if needed.
Once the migration is done, you can always set up the limitations to the original values if needed.