[exim] Dynamic email address

Hi all

I just received a weird request from our IT dept, that is on behalf of
our sales dept.

Basically the IT dept would like the new developed app to send out an
email to our client.
The email will contain a From: address of: booking123456@???
(random number after booking)

The booking followed by a random number will be needed for the client to
reply to the email.

I now need Exim to accept this email and then to forward it onto a file
(/var/bookings/).

If anyone can share some tips or advice it would greatfully be appreciated.

Kind regards

Brent Clark