typical email loads on a server
 

I have an IBM x-series server (1.8ghz, 512kb) and want to offer email to my web viewers and had a question about server loads. The server is running RH9 with qmail as the mail program. I have a phpBB web forum (avg 2,500 post/month). I was told that email really eats up servers.

If I were to have 500 users using email would this generate more than the phpBB web forum? If I use a webmail program like SquirrelMail will this make a difference? Thanks for your feedback.