[Exim] Rewriting From header.

[Pardon the unspecific subject, it was hard coming up with a short and
specific one.]

System: RedHat 7.2 on x86, compiled Exim 4.10 and Cyrus 2.1.9.

At our company we get support emails (for our home-grown applications)
sent to customerservice@???. Our customer-service people then
have multiple mailboxes in their Outlook Express mail-client of which
one is the customer-service mailbox and their From-address for that is
set to customerservice@???.

This situation is sub-optimal because we want to eventually move away
from Outlook Express (and the Windows platform); because if somebody new
joins the customer-service team we have to set up their From-address and
install Outlook Express; and because it really is a hack.

An optimal situation would be where all the customer-service people
subscribed to the customer-service.INBOX IMAP folder and read/replied to
mails found there. When the mail is then sent, the mail-server (Exim)
would figure out that this was a reply to a mail found in
customer-service.INBOX and as such would rewrite the From-header.

Is there any way we can do this? Or have you used a different solution
to solve a similar problem?

Thanks,

Erik.