Designating which Sent Items folder sent emails go to

Hello,

I've set up one of our computers to manage multiple mailbox accounts per
KB291626. This works great to allow our tech support person (Bill) to get
the emails submitted to the tech@ address while he's logged into his bill@
address. BUT, when he replies to the tech emails, the responses go to the
Bill sent items folder instead of the tech sent items folder. Is there a
way that even when he's logged into the bill@ account, the replies he sends
to tech@ emails go in the tech sent items folder instead of the Bill sent
items? Thanks.

Mark