We have purchased a company, and they will eventually be using our exchange server. We don't have control of their domain yet, but when we do we will change the MX records to point to our exchange server and add it to the list of accepted domains.
I've added all their domain accounts and email boxes, and just gave them our domain as an email address temporarily with the idea of going into exchange and adding the domain to the list of accepted domains when the MX records propagate and mail starts flowing here and changing their email address to that domain. My question is this: I don't want to add that domain yet to our accepted domain list because we still are sending email to a couple of people in that domain regularly, but for everybody else who won't even log into their box on our exchange server until we go live will it hurt anything if I just gave them their eventual email address now even if mail to that domain isn't flowing to our exchange server yet (I noticed that exchange server allows me to put anything I want for a new email address) and then simply add the domain to the list of accepted domains when we go live?
I guess the question in a nutshell is: does it hurt anything if I add an email address to a user in exchange if the address's domain doesn't exist in the list of accepted domains yet?