Where information for domain.com is stored when using qmail and vpopmail. When moving a domain from one server to another, or doing a backup and restore, make sure you include the following locations.

information storedcdbMySQL/PostgreSQL
tell qmail to accept mail for domain control/rcpthosts or control/morercpthosts (and control/morercpthosts.cdb after running qmail-newmrh)
tell qmail to deliver all mail for domain.com to user domain.com control/virtualdomains
tell qmail where to deliver mail for user domain.com users/assign (and users/cdb after running qmail-newu)
passwords and other user info for domain.com (--enable-many-domains) ~vpopmail/domains/domain.com/vpasswd (and vpasswd.cdb) table vpopmail (with other domains)
passwords and other user info for domain.com (--disable-many-domains) table domain_com
mail for user@domain.com ~vpopmail/domains[/x]/domain.com[/y]/user/Maildir/
forwarding info for alias@domain.com ~vpopmail/domains[/x]/domain.com/.qmail-alias
forwarding info for alias@domain.com when using valias n/a table valias (with other domains)