From the afterboot man page
Code:
Sendmail
OpenBSD ships with a default /etc/mail/localhost.cf file that will work
for simple installations; it was generated from openbsd-localhost.mc in
/usr/share/sendmail/cf. Please see /usr/share/sendmail/README and
/usr/share/doc/smm/08.sendmailop/op.me for information on generating your
own sendmail configuration files. For the default installation, sendmail
is configured to only accept connections from the local host and to not
accept connections on any external interfaces. This makes it possible to
send mail locally, but not receive mail from remote servers, which is
ideal if you have one central incoming mail machine and several clients.
To cause sendmail to accept external network connections, modify the
sendmail_flags variable in /etc/rc.conf.local to use the
/etc/mail/sendmail.cf file in accordance with the comments therein. This
file was generated from openbsd-proto.mc.
Note that sendmail now also listens on port 587 by default. This is to
implement the RFC 2476 message submission protocol. You may disable this
via the no_default_msa option in your sendmail .mc file. See
/usr/share/sendmail/README for more information.
From "/etc/rc.conf"
Code:
# For normal use: "-L sm-mta -bd -q30m", and note there is a cron job
sendmail_flags="-L sm-mta -C/etc/mail/localhost.cf -bd -q30m"