Paul Smith wrote:
Well, the sender should retry, but there is no rule about how often or
for how long it should retry, just a vague suggestion (not even 'SHOULD')
If gmail gives up after a few seconds, then I'm a bit dubious. I'd
expect it to try longer than that, I'd have thought for at least a day
(unless it gets a permanent error report back from somewhere).
Well, I have seen it number of time with non 24x7 SMTP customers
complaining about not getting mail and we found out that the senders
did retry - to a 2nd MX the customer had no idea was active, like his
ISP MX and from there it went no where.
So its possible Google tried to connect to his MX, failed, tried the
2nd MX and the transaction was done. Bob will never see it. :)