Small changes in the site layout can have large effects on your conversion rate. Surfers should always be just one click away from the sale on any page on your site. Include clear opt-out instructions in every mailing and mention those instructions at the top of every email. Mailing to this list can be occasional or regular. Some businesses generate most of their traffic with email.
Most mailings only produce a small surge in traffic for a few days after a mailing, however.
Generating a quality regular email letter is a full time job, but certainly it is one proven method of internet marketing. Many website hosting companies do not allow their clients to run software. If your host is like that, and you intend to build a mega-site, then move to a host that allows you to run scripts. Mega-Sites are defined by traffic. Any site with lots of traffic is a mega-site.