Basic
<a href="mailto:someone@yoursite.com">Email Us</a>
Adding a subject
<a href="mailto:someone@yoursite.com?subject=Mail from Our Site">Email Us</a>
Adding CC and BCC
<a href="mailto:someone@yoursite.com?cc=someoneelse@theirsite.com, another@thatsite.com, me@mysite.com&bcc=lastperson@theirsite.com&subject=Big%20News">Email Us</a>
Adding Body Text
<a href="mailto:someone@yoursite.com?cc=someoneelse@theirsite.com, another@thatsite.com, me@mysite.com&bcc=lastperson@theirsite.com&subject=Big%20News&body=Body-goes-here">Email Us</a>