[Exim] changing .forward : security question

I am installing a web page to allow my user to change their .forward
file.
What are the security risks in doing this, apart the user putting a
wrong address and losing all its mail ?
something ready ?
--
Leonardo Boselli
Nucleo Informatico e Telematico del Dipartimento Ingegneria Civile
Universita` di Firenze , V. S. Marta 3 - I-50139 Firenze
tel +39 0554796431 cell +39 3488605348 fax +39 055495333
http://www.dicea.unifi.it/~leo