EdgeTransport.exe consume memory on Exchange 2010

Hi all,

I am new to this forum and also new to Exchange.  We are using Exchange 2010 SP1.  It'd been working fine until yesterday.  Here is our summary:
   Exchange 2010 on MS server 2008.
   16 gig memory
   2 TB hard disk
   We still have plenty of hard disk space.
   
From time to time, it used up all 16gig of memory and lockup the server.  I see EdgeTransport.exe used memory from 2gig to 10 gig.  It will lockup the server for about 1 minute and then everything start to work again.  

I have tried:
   Install SP1 Rollup 4
   Order more memory
   Disable antivirus software.

   
Is there anything else I can try?

Thanks for all the help.