postfix or sendmail "tempting"

[<ago@hollo.idg.hu>]

Hi all!

I've got the job to make accepting mails to an e-mail 
address a bit unusual. What's unusual. I will explain. When
a mail arrives to the address it shouldn't appear in the
/var/spool/mail immediately. Because there is  daemon which
scans the mailbox all the time and as soon as it sees a mail
arriving it takes it from the box and passes it to a program
which works on it and then sends the output to a database. But
when the mail starts to arrive the system starts to write 
it to the disk immediately. ..And the daemon takes of , let's
say the first 15 bytes (From, mal client etc.) but not
whole letter. That's the problem because the body contains the
datas to the program. The only solution I see is to move it
temporarly to a /temp box or directory and as soon as the whole
mail arrived pass it to the accurate mailbox so the daemon could
catch it to delivery(the whole mail) to the program. Oh, yes,
and all the headers have to be untouched so the From and 
Reply to and Envelope _must_ be the same as they arrived. 
The ASCII art to this (as I imagine) :

mail to sms@example.com --> temporary box/dir(until closed) -->
--> sms@example.com /--> daemon --> program --> DB2/

How can I do it with postfix (preferable) or sendmail or any other
sendmail compatible MTA
RTFMs and HOWTOs are welcomed.
Thanx,
Ago