This was neat because you could change the address on a user and we could still figure out which user to reply to. So we decided we would route mail based on DN and mail would be stored as FROM: DN. But it promptly broke down if you moved an object in the LDAP tree. She (the object you just moved) gets a new DN, because she’s in a new location in the tree, and viola, she is essentially a brand new person, even if she has the same x400 or SMTP addresses.
3. Microsoft is versatile - surprisingly so for such a large company. Remember when MSN was at its heart a communications network which ran in parallel with the Internet, and was incompatible with it? MSN soon realised its error, and ported MSN over to the Internet, and made Internet access an integral part of Windows 95. Windows NT (much of whose code still underpins both current servers and desktop operating systems) was written without any consideration of Internet networking protocols, and Internet e-mail compatibility in the early versions of Exchange Server was nothing short of a kludge: the internal workings were based on the X400 protocol, and converters translated between X400 and SMTP (the standard internet mail protocol).. In short: Microsoft has made plenty of decisions which could be regarded as mistakes, but when it has realised those mistakes, it has been pretty agile at addressing them.
We have two set of users - students and staff. The students have their email address assigned by the default email address policy which sets both an X400 and SMTP address. This works fine.