Public Folders – Large Items – Failed move

This one is a new one for me, but I guess it should not be unexpected. If you’ve moved from Exchange on-premises to Exchange Online and your SMTP limits were higher than 150MB, more than likely you found at least one email that was greater than 150 MB … You may have even run into the rare mailbox move that was held up because of those large items and noticed this in your migration logs:

12/19/2019 2:19:31 AM [BN8PR19MB2916] Fatal error TooManyLargeItemsPermanentException has occurred.

For Public Folders, at least up until now, I have not had the same experience. Typically large items were not stored in my clients Public Folders. However, in one recent migration, they also had a large item (over 150MB) in Public Folders! This required a search and removal task for any other items over 150MB. Then I had to remove and restart the Public Folder migration batch. So the tip here is, check your mailboxes for those large items and if you have Public Folders, make sure to check those as well!

For those migrating Folders or mailboxes, you too can run into this issue believe it or not. I had a situation where a Public Folder migration stop because of an item that was too large. On-premises Exchange 2016 Public Folder migration – moving a folder to another mailbox. The item in question was 200 MB. Turns out that the Transport Limits for their environment were set to 100MB. Which means that any email over 100MB in Public Folders would not move. The solution? Increase the transport limit to a higher number – 300 /500 / 1000 MB – and then move the Public Folders again. Once the move completes, then set the limit back to the old number, which was 100MB in this case.

If you experience this, please leave a comment below! Thanks.