If while building a link, you choose as the Type, "E-Mail Link," then the bottom part of the Edit Link lightbox will provide you with the opportunity to fill in the e-mail address. You have two choices:
Type an ordinary e-mail address, such as "firstname.lastname@example.org" (without the quotes).
Type an ordinary e-mail address followed by a subject specification, in the format shown here: "email@example.com?subject=whatever subject you choose" (again, without the quotes).
When a subject specification is included (which we do suggest should usually be the case), the e-mail address you type must contain no spaces until after the first character following the "?subject=" (i.e., after the "w" of "whatever" in the example above). The subject text may contain the slash character ("/") with no special coding required. Often the path or path and filename part of the URL of the page the link is on will be an appropriate subject. Most browsers and e-mail software will place the subject you specified into the e-mail message's Subject field, and then provide the user the opportunity to revise it, if he or she wants to.