install procmail

preliminary notes

NetBSD and Debian/Ubuntu have /var/mail/ while Slackware has a symlink pointing to /var/spool/mail/.

Mbox format is the default. Maildir format starts with ., add trailing / and folder separator is .. MH format add trailing /.. A lock may be used with mbox (:0:) and probably MH as well, while it is not required for Maildir.

install

debian

apt install procmail alpine

slackware

slackpkg install procmail alpine

alpine linux

apk add procmail alpine

netbsd

pkg_add procmail alpine

from source

see procmail-source