Forum Discussion

ba50992's avatar
ba50992
Copper Contributor
May 12, 2026

Offboarding mailboxes fails with “PropTagToPropertyDefinitionConversionException.”

Hybrid M365 setup, just recently upgraded the on-prem server from Exchange 2019 to Exchange SE.  After doing so, migrations from Exchange Online back to Exchange On-prem fail at 10% with the error “PropTagToPropertyDefinitionConversionException.”  

I opened a case with M365 exchange support, and after some time, they came back to tell me that the Exchange Online portion of the process is not at fault, and that I have to engage the on-premise support team (this seems a little nuts to me, as its all connected and all supported, but I've been in this business for 30 years now, and it's not the first time I've seen buck-passing), and/or ask this community for help.

Hence, this post.

That error appears exactly two places on the internet, as far as I can tell: a blog (in German) from an Exchange expert doing cross-tenant migrations, and a page at 

https://west.jcteams.info/bhit11/docs/EX1232513.html that seems to describe my exact issue.  Neither had useful suggestions - mostly, they say this:

Set-MoveRequest -Identity "<UserPrincipalName>" -SkipMoving FolderRestrictions
Resume-MoveRequest -Identity "<UserPrincipalName>"

That didn't actually work, but when I tried the same parameters with Set-MigrationBatch, they worked as long as I ignored the message "The SkipMoving parameter is deprecated. Use the MoveOptions parameter instead. If you have any scripts that use the SkipMoving parameter, update them to use the MoveOptions parameter."  

So what was a simple process is now a more cumbersome workaround.  Does anyone have an idea on how to troubleshoot "PropTagToPropertyDefinitionConversionException?"

 

exchange online
Exchange Server
hybrid

1 Reply

  • Jamony's avatar
    Jamony
    MCT
    Jul 08, 2026

    Hi, a migration failing at a consistent percentage with a property conversion error usually means the move is hitting a mailbox item or property that Exchange cannot translate cleanly during the move.

     

    I would start with:

     

    1. Run `Get-MoveRequestStatistics -IncludeReport` and look for the exact bad property or folder.

    2. Try the move with a small bad item limit only if your policy allows it.

    3. Test with one affected mailbox and one known-good mailbox to see if it is mailbox-specific.

    4. Check whether the issue started only after the Exchange SE upgrade.

    5. Make sure both Exchange Online and on-prem endpoints are fully updated and healthy.

     

    If multiple mailboxes fail with the same property error after the upgrade, I would open a Microsoft case with the move report attached.