My answer wasn't going to be very helpful, because I have no knowledge of the subject, but in fact it turns out that if I try to reply to a Google+ mail message - which was showing with the address Someone's name (Google+) - it bounces with an error message saying that:
Delivery to the following recipient failed permanently:
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1 http://mail.google.com/support/bin/answer.py?answer=6596 f8si4338383icv.6 (state 14).
Google+ users may possibly want to be somewhat irate about this, since it is presumably not what this mailing procedure is intended to do. As it happens I don't seen to have an address for the person in question, and can't reply directly. Crap like this doesn't make me feel particularly kindly towards Google+
If have me in your circle / whatever please delete me, and just send me an email directly if you need to contact me.