I set up Ghost using DigitalOcean’s one-click image install about 2 days ago (Ghost Version: latest; OS: Ubuntu 18.04. I have set up with the Membership features with Mailgun and sent a test email. Right now I do not have Stripe integrated as I intend to use it mainly as a free subscriber list. I can send test emails via the Labs page, and have successfully signed myself up using 2 alternate emails with custom domains. However, when I try to sign up my normal gmail account, I get an error. I am completely at a loss as to why it wouldn’t be working with Gmail of all things.
My email address does contain periods (firstname.lastname@example.org) but even trying to sign up without the periods in the first portion of the domain does not work either.