vmail manages mappings from virtual mailbox e-mail addresses to the locations of their Maildir mailboxes and their IMAP/POP passwords. Data goes into /etc/courier/userdb, which must be owned by the domtool user for vmail to work properly. /etc/courier/exim (text version of mapping database) and /etc/courier/exim.dat (compiled DBM version) are root-owned, and DomTool uses domtool-publish with sudo to manipulate them.