Exchange 2010 – Remove AD User, Keep Email

The solution your third-party friend provided is very reasonable and is how I would proceed myself.

What I would not do is manually add additional SMTP addresses to individual user accounts, ever. If you did somehow need to maintain the old user's email address for forwarding to a new user after you delete the old user's AD account, I'd recommend creating a mail-enabled group with an Exchange Alias that matches the old user's Alias such that the group gets the same email address as the "old user". Put the user(s) who should receive those emails into that group.

(In general, you should use groups to assign additional SMTP addresses to users rather than doing it by hand. If you have turnover and need to give someone's replacement the same set of custom SMTP addresses as the "old uesr" you need only put the "new user" into the correct groups.)

You sound like you are on the right track. A disabled box can be attached to a new account.

See this link: http://technet.microsoft.com/en-us/library/bb232039.aspx

I think with the powershell objects you can force the disable and the cleanup that resets the box for reconnection all at once. See this: http://technet.microsoft.com/en-us/library/aa997210.aspx