I have fixed the issue with the html link/address box.
It will work with mailto now. But you have to replace all your whitespaces with %20 like the following.
This fabulous item is currently unavailable. Sorry about that! Please <a href="mailto:xyz@xyz.com?subject=Product%20reorder&body=Hi%20xyz,%20please%20let%20me%20know%20if%20you%20can%20order%20the%20following%20item:">email us</a> to find out if we can reorder it for you.
Please download the updated version from the following link.
https://www.essentialtexinternational.com/stock-message.zip
Thank you.