You can add a default subject and body to automatically appear in your mail client when you click a mailto link by:
succeeding your mailto link with a "?" and then optionally "subject=subject"(without quotes) and/or "body=body"(without quotes).
If you want to add both a default subject and body, join them with an "&" operator(without quotes) with no spaces in between.
For spaces between the words of your default subject and body, use "%20"(without quotes).
All together the syntax is:
Language: HTML
<a href="mailto:email@address.com?subject=a%20subject%20here&body=a%20body%20here">mail link</a>
you can paste the above line into an html file to see it working.
this would automatically add "a subject here" to your subject line, and "a body here" to the body of you email.