Yes. Great info. My understanding/small adjustment: Technically, messages stored for retrieval wouldn't be from the time of the outage - but from the time of the backup they restored from. (in my case, 4 days previous to the outage. this varies by server)
If someone had retrieved their messages already via POP, just before the outage, then yes they would be current as of that time. (but not IMAP)
Messages received in the 2 hours when the servers were down would probably re-try, but once the servers were online I believe the re-tries and any other messages coming in would be bounced back - since the accounts did not (yet) exist to receive them. I believe the message it was returning was:
550 Please turn on SMTP Authentication in your mail client. mail-qt1-f181.google.com [18.104.22.168]:38745 is not permitted to relay through this server without authentication.