Making a link to an email address is a little different than a normal link.
Normal links start with:
and email links start with:
A complete email link looks like this:
Make sure there is no space in the link at all and that the email address you use is correct.
You can link an email address to an email address or just some text, like "email us":
<a href="mailto:firstname.lastname@example.org">email us</a>