All of the standard mailto: tricks/links should work here as well.
# Address
mailto:someone@yoursite.com
# Address, subject
mailto:someone@yoursite.com?subject=Mail%20from%20Our%20Site
# Address, CC, BCC, subject
mailto:someone@yoursite.com?cc=someoneelse@theirsite.com,another@thatsite.com,me@mysite.com&bcc=lastperson@theirsite.com&subject=Big%20News
# Address, CC, BCC, subject, body
mailto:someone@yoursite.com?cc=someoneelse@theirsite.com,another@thatsite.com,me@mysite.com&bcc=lastperson@theirsite.com&subject=Big%20News&body=Body%20goes%20here.
iOS also appears to support the NTT Domoco MATMSG specification.
MATMSG:TO:someone@yoursite.com;SUB:Big News;BODY:Body goes here;;
