Hey Paul!
Thanks for swinging by the forum. That’s an excellent question, and it’s actually one we get pretty regularly.
The Plugin, like MailChimp’s hosted signup forms, would require using the double opt-in. We’ve found that this greatly reduces the potential for spam signups, and it helps ensure that you’re maintaining a list of opted-in subscribers. The article below goes into that process (along with the associated advantages) in greater detail:
The Double Opt-in Process: https://eepurl.com/gOG1
To have a single opt-in, I’m afraid it would be necessary to utilize the API or a 3rd-party plugin/form builder.
-Elliot