Craig White wrote:
You are correct of course, that nowhere does it state that sender MUST attempt to re-deliver. I do wonder if you would find an SMTP server that by default didn't attempt re-delivery on temporary failures to be acceptable. It MUST be configurable - that's it.
Okay, so Tim wasn't sure, but now we agree retrying, while it might be
good practice isn't essential.
I've just done a "host -t mx" for several companies. Most have four mail
exchangers, one had a dozen. While those are for incoming email, it's
likely that they generally have a similar number for outgoing email.
Without information, I assume that to be so. In many cases they will be
the same machine.
I don't know what their retrying policies are, but I can imagine that
retrying might involve an attempt by each of several machines, each
getting a 4XY response.
It might be a lengthy delay, it might result in email getting returned
to sender.
Tim is right in his belief that greylisting can cause delivery problems.
You don't have to think it's as big a problem as he does, but I don't
criticise him for seeing it as a risk he doesn't want to take.
Here is one list of recommended delays between retries:
http://www.mailenable.com/Help/Files/smtpdelivery.htm
The use of fake mx records suggested here looks enticing:
http://wiki.apache.org/spamassassin/OtherTricks
I discontinued using a second mx because it seemed only to receive spam,
and senders _should_ retry if I'm not listening.
--
Cheers
John
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