Conrad T. Pino writes:
 > Sendmail expects a lot from DNS and a "localhost"
 > entry in a DNS zone is one of them.

Just to report a solution in case someone encounters this and lives
(as I do right now) in a zone with no "localhost" entry in the DNS
records.

Use the following in your *.mc file (netbsd-msp.mc is used for the
distributions) when generating /etc/mail/submit.cf:

	FEATURE(`msp', `[127.0.0.1]')dnl

Explicitly including the IP address avoids DNS lookups, which will
fail in the case of missing "localhost" entries in the zone data.

Note that if this problem is at all prevalent in other domains, it
might be worth changing the distributed version of netbsd-msp.mc.

Cheers,
Brook