Help me understand "Default Reply To" address

Hi all,

I am confused. Please help. In Exchange 2010, if a user, for whatever reason, has TWO email addresses, how does that work? Here is an example...

I have a user named Rich whose email address at some point in history was "richs@domain.com ". At a later point it became "rlastname@domain.com" and that is his default reply address.

So... If someone emails him at the "richs@" address and he replies, does the reply go out as "rlastname@ "? And all subsequent replies are to that?

Am I wrong?

What else should I know? Sorry if this is a silly question that I, as a quasi-email-admin should know, but I don't. So... Help! Thanks!