🚀 go-pugleaf

ntm1169@dsac.dla.mil writes:
       After I post a letter, sometimes I see strange messages in response
       to the UNIX command "mailq."
	(Deferred: Host Name Lookup Failure)
	(Deferred: Connection timed out during user open with Shemp.C)
       What do these messages mean?  Does their presence have any bearing on 
       whether the mail will eventually reach its intended recipient? Are there
       any manauls or papers documenting these and other mail messages?

The ones you mention are pretty harmless.  "Host Name Lookup Failure"
means that your nameserver went looking for the address of the
intended destination host, but nobody answered.  For example, it might
not have been able to reach the root servers, or else one of the
servers indicated by the root servers was not reachable at the time.
"Connection timed out with <whomever>" means nothing more than that
the intended destination host isn't "answering the phone" at the time.
Your mailer should be set to re-run its outbound queue from time to
time, and it will try then to reach the host.  It's a per-site
configurable option as to how long to keep things sitting in-queue
before giving up and returning the mail to the sender as
undeliverable.  It's generally on the order of a few days; mine is set
for 5.

There are others, of course.  "Bad file number" is a classic item;
when it means anything (which is rare, due to old bugs with the
tendency to use errno at inappropriate times), it refers to the fact
that the SMTP session to the remote end was lost midway through a
conversation.  Again, normal queue runs by the mailer will see to it
that the mail keeps trying to get where it's going.  I don't think
there's any definitive list of such messages, though.  When all else
fails, "Use the source, Luke."

--Karl