This error message can frequently appear for users after the mailbox migration from Exchange 2010 to 2013 or 2016.

The actual cache is that this error will be coming up only for few users and it appears to be perfectly fine for rest of the users. The thing is that the Outlook will appear to be working fine, users will be able to send/receive emails except for this annoying message keeps prompting the users very often.

On Further Analysis identified that this occurs only for users who have multiple delegated accounts mapped under Outlook. The user mailbox resides on a different database and the mapped delegated accounts reside on different databases.

The delegated account has not fully established the connection to the new mailbox databases after the migration due to some reason and the user's delegated mailbox table did not receive the delegate permissions accounts information. We can further look at a deep analysis on the mailbox tables on the affected user by using MFCMAPI  and looking into ACL tables but then that will consume a lot of time.

Mostly the below two solutions will  fix this issue:

1) Recreate the Outlook profile which will re-establish the connectivity to the new databases for the delegated accounts and update the mailbox table for this user.
2)Moving the mailbox to a different database which will reset the mailbox table receive folder values, update the ACL tables for delegate accounts and solve the issue.

But still not sure what is causing this issue. Also there is one more possibility which might cause this issue. The msExchHomePublicMDB attribute on Exchange 2016 databases should not have the legacy public folder object (Exchange 2010).

If we find this value in Exchange 2016 databases we can go ahead and remove them since there are no more OAB end points that depend on PF’s and no more Outlook clients that require PF’s in Exchange 2013, 2016 Environment.

In order to remove them perform these steps:

Open ADSIEDIT.MSC – Configuration Container – Navigate to Configuration Container – Expand Services – Microsoft Exchange – Domain – Administrative Group – Exchange Administrative Group – Databases – Right-click on the databases seen on the right pane and choose properties – Look for msExchHomePublicMDB and if it has any values clear them. Make sure to clear these values for all the other databases we have.

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Very Important note:

This above troubleshooting is applicable only for users migrated from Exchange 2007/2010 to 2013/2016 and not for the below scenarios in any cases.

  1. Issue occurs after the mailbox was moved to a new Exchange site or forest with same Exchange versions Exchange 2010.
  2. Issue occurs after Changes were made to the public folder databases in Exchange 2010.
  3. Issue occurs after Changes were made to the Exchange server endpoint.
  4. Lync wasn’t restarted after the mailbox was moved or after the Exchange server endpoint was changed.
  5. You’re running an older version of the Outlook client.
  6. The service re-balances mailboxes on databases at various sites.