Ever since our organization migrated to Exchange Online we noticed a flaw with how Outlook's Auto Complete list (nickname cache) operates. We've finally gotten a confirmation from Microsoft that the following is indeed a problem:
- Each entry in a user's local Outlook auto-complete cache is represented by an LDAP distinguished name.
- When Exchange is hosted on-premises these entries pretty much never change.
- When your organization is hosted on Exchange Online, the distinguished names for your mailboxes can change without notice due to maintenance processes (Microsoft's engineers have confirmed this to be true).
- There are other ways that a mailbox's distinguished name can change (re-creating a mailbox, etc.)
- Outlook's local auto-complete cache has no way (currently) to reconcile changes should any of its entries' distinguished names change in the cloud.
When the entries in the local auto-complete cache become "stale" the following may happen:
- Emails to affected recipients can bounce back.
- Emails to distribution groups containing members which have stale auto-complete entries can bounce back.
- On occasion no NDR is even generated (BIG PROBLEM).
As noted above, we've gotten Microsoft to admit that this is indeed a problem with Outlook when combined with Exchange Online. I was told that the Outlook product team has been notified of this problem. However, in order to escalate this issue I was asked
to spread the word to other customers so they can also chime in if they've been affected.
Please supply your feedback to Microsoft and ask that Outlook be enhanced to either reconcile the local auto-complete list with the online GAL, or provide some sort of notification to the user that an auto-complete entry has become "stale" or invalid.
Thanks for everyone's time!