I am setting up a multisite network and wondered what you

I am setting up a multisite network and wondered what you guys normally do about email?
I don't want to use Google Apps in this case because it would be too expensive.
I want each site to be able to have emails eg: me@site1.com - however site1.com will be mapped to site1.mysite.com - and won't have a cpanel...so how do i go about setting up email for my clients?
Thanks