Hey Yall,
So I ran across this today, I had a customer who was creating marketing emails out of D365 and the hyperlinks were not working, they'd convert themselves back into anchors.
I checked, and didn't find a lot of information on the actual parameters of the URL requirements, so we worked backwards. I gave it bad data, different links, etc. and through testing, I've found that the link has to be an http://, cannot be an https://.
In our use case, we were using YouTube videos with links, and a file that auto-downloads for the users who click.
Hopefully that works for you guys! Cheers!