On Tue, Apr 22, 2003, Vernon Schryver wrote:
In practice, those words are understood as applying only to a single "queue
run" or attempt to send a message. An SMTP client tries the MX servers
By whom?
for a domain name until it finds one that answers the TCP SYN. It then
tries to delivere the message. If it receives a 5yz result, it forgets
entirely about the message (except for the exception that is treated like
a 4yz result). If it receives a 4yz result, it saves the message but
forgets all of the details of its efforts until the next "queue run."
Your notion is based on one or or both the obviously bad ideas:
1. STMP clients treat a 4yz as needing an immediate retry at another
SMTP server. This is obviously bad because 4yz responses mean
"try again *LATER*." MX RRs often point to the same host (e.g.
when it is multi-homed) and even if not, trying again immediately
at an SMTP server related to one that has said "I'm too busy try
again later" violates the spirit of "try again later."
8.12.0/8.12.0 2001/09/08
...
If sendmail receives a temporary error on a RCPT TO: command, it will
try other MX hosts if available.
You may want to check other MTAs. AFAIK only qmail behaves the way
you describe. The RFC is unfortunately not clear in this point.
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