nice.old.couple+alice@gmail.com
nice.old.couple+bob@gmail.com nice.old.couple+alice@gmail.com
nice.old.couple+bob@gmail.comEdit: sendmail and qmail, too, apparently: https://www.cs.rutgers.edu/~watrous/plus-signs-in-email-addr...
Easier to remember than a username because it's guaranteed to not be taken, so you can use the same email everywhere: email+name@provider.tld. Where as "alice" probably is taken.
Also should work with any email provider, it's part of the standard.
If the intent is to allow two people to have independent accounts even while using an email they both control, offloading that to the email protocol seems broken to me. It's the exact same email address from the perspective of security. Anything coming after the plus sign should be ignored for the DB key, but kept around for sending emails, so it can still be used for filtering those emails (for convenience, not security). So they could sign up either as
alice <couple@notgoogle.com>
bob <couple@notgoogle.com>
or as alice <couple+alice@notgoogle.com>
bob <couple+bob@notgoogle.com>
but that difference should only ever matter for their email filtering, not for identifying them.