Short post to describe some interesting behaviour I noticed in Exchange 2013 EAC.
If you match a rule such that “Apply this rule if… The recipient is…” and you choose a single alias of a mailbox, you’ll see only the alias selected in the Rule dialog box:
However, when you save the rule, close the dialogue and reopen it, you’ll see that the entire mailbox is now matched:
I assume that this is a well-known piece of Exchange information – that messages to a mailbox’s single alias cannot be rejected while allowing messages to the mailbox’s other aliases – but it took me by surprise as it was not what I expected. Sure enough, all messages to the mailbox using any alias were rejected when I tested this.
Of course, I realized this a day later, wondering why I wasn’t receiving deliveries… Oops.