1. Edit your Template
2. Now find out
post-footer-line post-footer-line-3
( press 'Ctrl' + F to open your browser's search box)
In some template , you will find out a code line as
<div class='post-footer-line post-footer-line-3'>
and in most of templates , you will find out a code line as
<p class='post-footer-line post-footer-line-3'/>
Now change these code lines by giving your information
<a href="mailto:Type Your Email Address here"><img src="Image URL of your Image" alt="Email me" /></a>
* mailto: is essential
Ex:-
<a href="marhabano1@gmail.com"><img src="http://sites.google.com/site/dragonzstore/_/rsrc/1242179856980/Home/email%20me%201.PNG" alt="Email me" /></a>
Now paste it below the code line
<p class='post-footer-line post-footer-line-3'/>
Now you will see a image link like this
Email me
If you don't want a image, then add this code
<a href="marhabano1@gmail.com">Email me </a>