A couple of months ago, a customer sent us a ticket, complaining that a mail group was incomplete. Specifically, his manager was not listed among the recipients. The mail group in question contained all managers, and membership was gained through dedicated active directory (AD) organisational units (OUs), one for the manager of each business unit (BU). I checked the Exchange address book in Outlook, and sure enough; the manager group for his BU was not listed among the recipients.
I decided to dig deeper, and checked AD. The mail group was managed through AD, and all manager-OUs – including the one that did not show up – were members. I double checked the specific OU, and found that it was not only active, but listed the appropriate manager as the sole member. I then checked Exchange, and found again that the manager-OU in question was a member of the group. Consulting with a colleague, I learned that they had had an issue that emails were sent to the email address for the manager-OU, rather than the group email address, and that they had requested that the address be hidden from the Exchange address book.
With this fact in hand, I had a working hypothesis. I checked the manager-OU in Exchange, and found that it had indeed been hidden from the Exchange address book:
Once this had been ascertained, it was a simple matter of undoing that change, and telling them that they couldn’t have it both ways, and that they should talk to the people sending emails to the wrong list.