why outlook express can send out a oversized email to crash our exchange 2000 email server ?   

Dear sir/miss ,

My company is using the exchange 2000 server , and some users are using of 
microsoft outlook , some users are using of outlook express.
I had set the in & out sized quota for each users (10Mb in & 10Mb out ).
But there have a very big problem of that , each time when a outlook express 
user whom sent out a oversized email (may be 100Mb),
our email server must be crashed down ( all outlook express users can't sent 
out & receive of emails , but the microsoft outlook's ok).

We need to reboot the server & find out whom had sent out such a very big 
email & delete it from a microsoft outlook workstation, else , when the
use use outlook express again , the email server could be crashed down again 
& again.

Why ? Could any person tell me how to block such users to send our a very 
big oversized email send out by outlook express or how to fix this big 
problem ? Thanks so much !

Sam Mok
2008-04-18

date: Fri, 18 Apr 2008 11:26:23 +0800   author:   Sam