Insert a line break in mailto body

I would suggest you try the html tag <br>, in case your marketing application will recognize it.
I use %0D%0A. This should work as long as the email is HTML formatted.

<a href="mailto:email@mycompany.com?subject=Subscribe&body=Lastame%20%3A%0D%0AFirstname%20%3A"><img alt="Subscribe" class="center" height="50" src="subscribe.png" style="width: 137px; height: 50px; color: #4da6f7; font-size: 20px; display: block;" width="137"></a>


http://stackoverflow.com/questions/22765834/insert-a-line-break-in-mailto-body