how to transparently resend email?

Sendmail 8.12.10+Sun/8.12.10
solaris 9

got a bit of a wierd request so bear with me please :-)

we run a sendmail server running the versions of software above.
some users have .forwards to 3rd party email accounts ie email comes
in, then gets forwarded out to blackberries and home accounts etc.
a user has "lost" some emails on said 3rd party accounts and would
like them resent. (user doesn;t really very often vsisit office to
handle email directly "in-house").

we can esilt find/grab/isolate the emails from the last three days
(say) but just using "tail" on user's /var/mail/ - no big
deal. We can also reasoinably esily seperate all the individual
emails similarly.

However.... how can we resend/forward said emails such that they
arrive at blackberry/home/etc as if originally snet? Colleague
suggested that all we need do is cat the tailed emails onto the /var/
mail/ - but that wouldn;t invoke the .forwards ....
colleague also suggested catting the tailed emails onto HIS /var/mail
file which would "introduce" them to his inbox from which he could
then forward to the user's account (from which they can then
be .forwarded)... but of course that would mean they arrived with HIS
name on them not the originators (which would be a problem as it turns
out).

So - is there a way we can "reintroduce" emails such that they get
sent as per .forward and arrive as if they had been sent by the
otiginator/

cheers (and thatnks for your patience)

ian