How do I add a subject to my e-mail link?
While people have suggested that [?subject:] will add a subject to your e-mail, it is not a valid e-mail address and will cause the e-mail to disappear without being sent in some e-mail clients.
<a href="mailto:firstname.lastname@example.org?subject:your+subject">e-mail me</a>
As stated in http://www.w3.org/Addressing/rfc1738.txt:
A mailto URL takes the form:
mailto:<rfc822-addr-spec>where <rfc822-addr-spec> is (the encoding of an) addr-spec, as specified in RFC 822.
Alternatively, the attribute [title=""] is a suggested way to add a subject. It is a valid HTML 4.0 attribute and will not cause the e-mail to disappear in e-mail clients that do not support it:
<a href="mailto:email@example.com" title="your subject">e-mail me at firstname.lastname@example.org</a>