Or add a footer to the message showing the address it was sent to like is now done for regular posts.
I like that choice.
Note: the approval email *is* addressed to the owner, perhaps it should have a footer also that says "Login to <email address> to administer your new group." or some such...
... or some such. Said that tersely the user might think it means to log in to their email service.
The wording needs to be clear that the user needs to log in to Groups.io, putting that email address in the Email Address box on the Login page.