No, you can make the configs (both) use a deferred DNS.
You could even tell submit to accept unresolvable hosts
and listen only on 127.0.0.1 and ::1 (ipv6 localhost) if
you trust the users on your box (presuming a home server, here).

Normally, you'd want to pass the "no such host" message immediately.
DNS lookups are good for that.

See the cf/README and op/op.txt (which you might have to make(1)).



Quoting Pavel Cahyna (pcah8322@artax.karlin.mff.cuni.cz):
> > 
> > you're getting the dns timeout because you're off-line.  when you're
> > off-line, sendmail can't look up (or verify) the existence of the
> > address to which (or from which) you are sending the mail, so it stays
> > in the client queue.  when you go back on-line, then the dns lookups
> > can work again, so the queue can be flushed.
> > 
> > this is perfectly normal behavior.
> 
> So, you need DNS working even for the local mail delivery from cron to
> root? Doesn't seem to be good.
> 
> Bye	Pavel