After mailbox is migrated back from EXO to your on-prem Exchange organization, user can experience issue while logging in to OWA with error below:

From my experience, in most cases this error can be resolved by removing 0x36460102 attribute for inbox folder via MFCMAPI utility.

MFCMAPI provides access to MAPI stores to facilitate investigation of Exchange and Outlook issues and to provide developers with a sample for MAPI development.

Usually, this utility should be run on computer with Outlook installed. Mailbox that we need to connect, should be added to Outlook profile – as new one, or additional mailbox with full access permissions to existing profile.

More information on MFCMAPI here.

If you have 32-bit version of MS Office, you will need 32-bit versions of MFCMAPI, for 64-bit accordingly.

💡Note. Use MFCMAPI on your on risk. Incorrect usage of this utility can corrupt mailbox content.

1. 🔗Download MFCMapi tool

    2. Before performing any step, it’s highly recommended to make sure, that Outlook client configured for this mailbox is not running somewhere else as simultaneous access to the same elements in a mailbox can cause collisions and different type of issues.

    3. Open MFCMapi on the machine used by the user – we will need the Outlook profile to open the store with this tool. Alternatively, you can run run MFCMapi on any computer with Outlook, where problematic mailbox is added as additional mailbox to existing profile or via new profile (you should have full access to it).

    4. If Outlook profile is configured to use Exchange cashed mode, in MFCMAPI go to Tools -> Options -> and tick the boxes for Use the MDB_ONLINE flag when calling OpenMsgStore and Use the MAPI_NO_CACHE flag when calling OpenEntry options. Or you can reconfigure Outlook to use online mode (usually, restart of Outlook is not required).

    5. Click Ok

    6. Then go to the main menu Session -> Logon… -> and choose the Outlook profile used by user (or profile that has additional mailbox connected).

    7. Select the store for user’s mailbox from the list and double-click to open the store. On the new page that is opened, expand Root Container, than Top of Information Store and select Inbox. You will be able to see entries on right panel. Select the value which has Tag Value of “0x36460102“, write-click and delete this tag.

8. Right click on the Root Container and choose Open associated contents table.

    9. Ask problematic user to log into OWA and check if issue is resolved. If it’s not, proceed with steps below.

10. On the Hidden Contents table tab (opened windows title), arrange the columns header and scroll to the right until you can see the Message Class details for each entry. Example:

    11.  Deletion steps: Right Click on the Message Class -> Delete message -> Permanent deletion (delete to deleted items retention if supported) and click OK.

Repeat deletion steps for the below entries, if they exist:

• IPM.Configuration.Agregated.OWAUserConfiguration
• IPM.Configuration.OWA.SessionInformation
• IPM.Configuration.OWA.UserOptions
• IPM.Configuration.OWA.ViewStateConfiguration

    12. Once the above steps were performed, close the MFCMapi using the X button on the right top corner.

    13. Login to OWA and test if the issue occurs.

⚠️What’s it all about?

These attributes\properties are related to OwnerLogonUserConfigurationCache and contains cashed metadata like Search History, Calendar Information and etc.

Theoretically, this property can be removed \ cleared via EWS (Exchange Web Services) custom script, so there’s no need to connect to mailbox via MFCMAPI. Please, refer to corresponding documentation on how to do that programmatically:

🔗Deleting custom extended properties by using the EWS Managed API 2.0

There is also an option to delete this information proactively before offboarding on Exchange Online side using Exchange Online PowerShell.

Example:

Remove-MailboxUserConfiguration-Mailbox user@domain.com -Identity “Configuration\IPM.Configuration.OWA.UserOptions”

Remove-MailboxUserConfiguration-Mailbox user@domain.com -Identity “Configuration\IPM.Configuration.OWA.NonBootUserOptions”

Remove-MailboxUserConfiguration-Mailbox user@domain.com -Identity “Configuration\IPM.Configuration.OWA.OtherMailbox”

Remove-MailboxUserConfiguration-Mailbox user@domain.com -Identity “Configuration\IPM.Configuration.OWA.ViewStateConfiguration”

In case you want to use the above solution, I recommend trying it out beforehand and making sure that no critical information is being deleted (for example, you can consider autocomplete cache can be useful).

Apparently, the problem is caused by an incompatibility between the data format in the cloud and what can be stored in on-prem.

End.