We recently had some strange problems with the Outlook Offline Address Book (OAB)

Scenario

My company has two domains management.contoso.com and name.contoso.com. Both of those are fully functional separated Active directories with an Exchange infrastructure.

My User has this setting:

But only the [email protected] is set up in Outlook. The [email protected] mailbox exists due to historical reasons.

Problem

After sending an email to [email protected] the following happens:

Diagnostic information for administrators:

Generating server: exchange.name.contoso.com
IMCEAEX-_O=FIRST_ADMINISTRATIVE_GROUP_OF_MANAGEMENT_CONTOSO_COM=Recipients_cn=user2@name.contoso.com
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##

Where user2 is the internal username of user2 in management.contoso.com…

Well thats a problem. Apparently Outlook looks up user2 in the management.contoso.com even if the management.contoso.com account isn’t set up in Outlook. It seems enough that the Exchange account exists in the first place.

After trying some stuff we narrowed it down to the OAB

Solution…ish

This little script deactivates the automatic download of the OAB and deletes the local copies of it.

The Problem with this is that you can still manually download the OAB.

Furthermore: Every broken address stored in the Outlook AutoComplete needs to be deleted and typed in again manually.