Hi @Mettem, 

Thanks for sharing your question with us! I can definitely understand wanting to know how to do this is the new editor, happy to help! 

You can add the default  subject line and body you want to auto-populate into the link itself. The formatting of the link would be like this:

mailto:youremail@example.com?subject=Your Subject Line&body=Your Message Content

You would add the desired subject line after subject= and then add your body content after body=, replacing what is in the example. This will allow your subject line and body content to populate in the email that is opened! 

Thanks for participating in the Community!

-Taylor 

Just to add to @Taylor Tarpley comment, I like using this little tool (no affiliation) to generate mailto code that you can quickly copy/paste into your email template (just remember to paste as source).

https://mailtolink.me/

Great, thank you both for your help!