We (MSF) have found that many new users never receive their confirming email within the 20 minutes allocated time. We are told that this is a well documented problem.
I created a Captive Server at home, and when I test and query Postfix, I see that many GMails apparently never leave my captive server. I get a "D37174BC283 716 Wed Jun 13 07:10:16 validation@wifidognetwork
(connect to alt1.gmail-smtp-in.l.google.com[72.14.215.27]: Connection
timed out)" message.
I think that a useful "new feature" could be added where we have an option to add a .cc copy to all confirmation outgoing emails. We could send them to a monitored email account. This would allow us to easily see if the problem is at the customers end (we see the confirmation .cc copy in our monitored email) or at the server (as above, if the Connection timed out, a copy would not be seen in our monitored email account.
