If you have tried using the AddThis button on your web site, you may not have seen an “email” option displayed, even if you had it in your list of sharing methods.  It is important to note that the username is required by the button for email to be enabled.

On a separate note, there are better options specifically for email sharing that easily allow for your own branding and high delivery rates, but AddThis does a nice job combining all into an easy to use and implement solution, with a small footprint.