This worked for me when I did the following.
Created a test program.
Created a rich text My Token (my.Registration Link) with our corporate website as the only value in the Rich Text Editor (http://www.conductor.com).
Created an email in the program.
In the Email Designer, selected a section of text (Send and invite to your friends), clicked the Link took and added "mailto:?subject=Join me at this event&body=Hey, I just registered for this event. Join me: {{my.Reistration Link}}" in the Link URL field and clicked Update.
Saved and approved the email.
Sent the email to myself and clicked the link. I received the email below and the link worked.