install dovecot as package binaries

debian

apt install dovecot-imapd
grep dove /etc/passwd
grep dove /etc/group

gives

dovecot:x:111:120:Dovecot mail server,,,:/usr/lib/dovecot:/usr/sbin/nologin
dovenull:x:112:121:Dovecot login user,,,:/nonexistent:/usr/sbin/nologin

dovecot:x:120:
dovenull:x:121:

slackware

slackpkg install dovecot libunwind libsodium mariadb sqlite
grep dove /etc/passwd
grep dove /etc/group

gives

dovecot:x:94:94:User for Dovecot processes:/dev/null:/bin/false
dovenull:x:95:95:User for Dovecot login processing:/dev/null:/bin/false

dovecot:x:94:
dovenull:x:95: