System emails not being sent from preview branch instances

I have a project where I am utilizing the new branching feature (amazing!! love it!!) but I've noticed, that system emails aren't sent if I, say, sign up a user on a branch instance. I have a custom SMTP provider set up correctly, so I doubt this is the issue.

Maybe this is by desing, in which case it's okay, I'd just like to confirm with someone. Thanks in advance!