Visit the page http://demos.telerik.com/aspnet-ajax/editor/examples/overview/defaultcs.aspx and create a hyperlink including the tool tip and the press ok.  You should end up with something similar to:

Copy Code <a href="http://www.microsoft.com" title="please click on me">Microsoft</a>

Now, edit the link and switch to the email tab and enter in an email address and click on ok.  You should end up with:

Copy Code
<a href="mailto:info@telerik.com" title="please click on me">Microsoft</a>

Note, the title attribute has been carried over from the information on the hyperlink tab.
There should be a tooltip field to the email tab.