The message exceeds the maximum supported size., Cannot save changes made to an item to store.

Hi David, sometimes the max message size limits have been modified on an individual mailbox and do not match the default size limits for the tenant.  For example, the source admin might have increased the allowed sizes for a single employee who handles large contract documents. 

I recommend running the "Collect Statistics" task for mailboxes in ODM and selecting the option to "Collect statistics from target".  Shortly after this task completes, you will be able to download a Comparison Report from the task details.  Find the mailbox in this report and compare the Max Send Size Allowed and Max Receive Size Allowed for that specific user.  If target is smaller, then you can increase the target size allowance for that mailbox, or inform the user that large items will not be migrated.

Thanks Becky. I saw from my spreadsheet that one mailbox had different send and receive max sizes. I appreciate that.

Thanks Becky. I saw from my spreadsheet that one mailbox had different send and receive max sizes. I appreciate that.