Virtual domains functionality in Postfix provides a means to redirect messages to different locations by altering the message envelope address. The header address is not altered by a virtual domain mapping. While some functionality of virtual domains overlaps with features available in aliases, virtual domains can be used for local or non-local addresses, while aliases can only be used for local address.
Much like aliases tables and canonical mapping tables discussed in the previous sections, this is simply the path to a file containing the mapping tables for virtual domains. This is usually something along the lines of hash:/etc/postfix/virtual, and must be converted to a database format for use in Postfix. Webmin will perform the database generation step for you.