[EXIM] How to add date&time to the subject ?

Hi,


I'm a new in exim.
I want to add date and time to the subject to all incomming mails in the
form of
"this is the old subject" -> "[YYYYMMDD-HHMISS] this is the old
subject"
But all replys to a "changed" Mail should not be converted.

Can anybody help me?
How to do this ?

regards,
Rainer