cacert-devsetup/docker/imap_plain_userdb.conf

passdb {
  driver = passwd-file
  args = username_format=%n /etc/dovecot/imap_user.txt
}
userdb {
  driver = passwd-file
  args = username_format=%n /etc/dovecot/imap_user.txt
  default_fields = uid=catchall gid=catchall home=/home/%n mail=maildir:/home/%n/Maildir
}