Typically, left clicking a link opens it. In the case of the email address that shows on our messageboards, it is also a link. Left clicking it should open whatever your default email program is ready to send a reply or message to that address.
EXAMPLE OF CODE
For John's response clicking his email address activates this link code -
(a href="mailto:email@example.com?subject=Re: OT computer - email")firstname.lastname@example.org(/a)
NOTE - the <> were replaced with () to display the actual code and not have it look like this clickable link -