For example I want to add a subject in a mailto: link using MB custom fields. I'm using the Email field, but it won't accept the ?subject=AboutMyWebsite after the actual email address.
I tried adding the attribute sanitize_callback = none on the Email field, but that didn't work.
Maybe I need to add another field for the email paramaters and then combine them somehow to form a clickable link or a button link.
Any suggestions?