It would be really helpful to add a reason code to the Do Not Mail setting in Addresses. Currently, if an address is marked Do Not Mail, it is difficult to know whether it was marked that way because of donor communication preferences or if the address is no longer valid.
It's actually worse than that. Do Not Mail is commonly used as a Solicit code in RE7, but when you mark an address that way in NXT, it marks the record in RE7 as "Has no valid address. The developers have a mess on their hands with this one.