with:
install: etcsubmit.cf: stat: no such file or directory

seems to be command:
# install //etc/mail/submit.cf
STRIP=/usr/tools//bin/i386--netbsdelf-strip /usr/tools//bin/nbinstall -N /usr/src/etc -c -r -o root -g wheel -m 444 etcsubmit.cf //etc/mail/submit.cf

This is on 3.99.3, as the kernel reports, sources of today.
Could not find(1) anything submit.cf-ish.