NM: Warning: BTMapiMessage Save Changes --MAPI Object Changed 80040109 (B303851)

Issue

Over the past few months we've been migrating users with no issues. Yesterday, we started seeing this error on all migrations:
Error code 80040109
We've confirmed we aren't hitting any mailbox size constraints, or retention settings. No Antivirus is running on Exchange or the farmhands.

! Error: Saving Properties --Error code 80040109 Folder:

or

# Warning: BTMapiMessage Save Changes --MAPI Object Changed 80040109

 Solution

This is an error from Exchange (not an issue with the migration engine or process), preventing the migrated message from being saved. This means Exchange tried to modify the migrated message before the message could be saved by the migration engine.

Confirm Antivirus and Retention policies are not a contributing factor.

Make sure "Message Rate Throttling" is disabled on the Exchange server.

Here are the details from Microsoft regarding this feature:

Message Throttling Scope

Message Throttling Options on Transport Servers

Message Throttling Option on Send Connectors

Message Throttling Options on Receive Connectors

Message Throttling Policies

User workload management in Exchange 2016‎ 

Our product is working as designed, please contact the Exchange administrator or Microsoft to troubleshoot and resolve this issue.