Notes to self on the Exchange 2010 email address policy.
One – if you have multiple email address policies only the one with the highest priority applies. This is obvious in retrospect but easy to forget. For instance you may have a default policy setting a certain email address template. And you have another policy, applying just on a particular OU. Also the latter policy has a higher priority than the default policy. So you may expect that the primary address template set by the OU specific policy will be the default primary address and the address templates set by the default policy too are present. Nope! Whichever policy wins, only that is applied. Email address template from the other policies are ignored.
As a corollary to this, if you want the default address templates too to be used when another policy wins, be sure to add the default email address templates in this other policy.
Two – removing an email address policy, or moving a user to another OU so that it falls out of scope of a particular policy, does not mean the email addresses defined by that policy are removed. Nope! They continue to exist, just that the primary address will change (to that set by the next policy that wins as the default). Again, in retrospect this is sensible. This ensures that users continue to receive emails at their previous email addresses. Without such a behavior when users move OUs and fall out of scope from a particular policy, their existing email addresses will get removed and they’ll stop receiving emails at that – probably not something you expect or want.
If you want the existing email addresses to be deleted, use PowerShell.