🚀 go-pugleaf

You're correct in that a temporary-failure result from the resolver should
result in requeueing a piece of mail for a later delivery attempt, and this is
indeed how things work when it's sendmail doing the resolver calls (e.g.
looking for MX records or A records to do the actual connection).  The only
silly thing is in the $[ $] interface itself; all that happens is that sendmail
makes an attempt to canonicalize the name.  (The as-distributed version of the
underlying C routine doesn't even return a success or failure code.)  That is,
there's no way that the person writing the sendmail.cf file (in which the $[ $]
appear) can determine whether the resolver call succeeded or failed, and if it
failed, whether it was a transient or permanent failure.  The hack of adding
the ``.'' and seeing if it stayed around is only an attempt to determine if the
resolver call succeeded at all, and confounds the resolver's use of a sequence
of ``default domain suffixes''.  Nobody has yet invented a mechanism whereby
the sendmail.cf program can query the result of the resolver call--except for
perhaps the IDA sendmail kit.

You might argue that sendmail should look at the result of the
get-canonical-name routine and handle some of the failures itself; you could
argue that if it were to get a temp failure on any $[ $]-spawned resolver call,
that it should bypass sending to this addressee for now and move on to the
next.  Maybe that's reasonable.  Is that what the existing sendmail.cf
files/programs expect to happen?  Should all $[$] requests be assured of
working before trying the first delivery?  (What happens if a
partially-qualified domain name escapes *your* site?)  How should sendmail deal
with permanent failures--by rejecting the address as invalid?  Hardly.  Might
there be an answer to all these questions?

                Craig Everhart
                Andrew message system