sendmail is in my opinion unessisary advanced and compicated for the most installations and there are a more simpler solution already in base for OpenBSD which is smtpd. This daemon is not active by default but it’s simple to change.
Edit /etc/mailer.conf and change to the following
Rebuild aliases database
Make sure smtpd starts with the system and stop sendmail
echo “sendmail_flags=NO” >> /etc/rc.conf.local
echo “smtpd_flags=” >> /etc/rc.conf.local
Modifiy /etc/mail/smtpd.conf for your system, it’s a dream in comparison to sendmail
– Johan Ryberg