> Sendmail uses no authorization, and it is unlikely that "sendmail" qua 
> "sendmail" is the issue. Maybe you should try watching the interaction 
> on the wire. tcpdump is your friend. :)

While not authentication per-se, sendmail does try to probe DNS for
all sorts of stuff.  If DNS is misconfigured and/or /etc/resolv.conf
points to a broken DNS server one can get considerable delays.

It's also possible that the delays are caused by the remote sendmail
trying to validate the senders IP address or do a forward lookup to
see if the observed address really belongs to the claimed host.

-wolfgang