CertSimple will be shutting down on January 30 2020. Read the announcement here.
One of the standards used to verify control over a domain is the 'admin@' email address. This is normally set up as part of creating a domain - pointing to the site's administrator - but not always.
If you prefer not using email, just ask us for file upload verification or DNS TXT verification instead!
If you want to use email, and use Google Apps (which Google sometimes call GSuite), you can easily add an alias.
From Users, click a user. Then click the Account, Aliases, Add an alias.
Then ask us to resend the domain control emails!