Virtual Domains

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Virtual domains are similar to the multiple host names discussed in the previous section, but there are some important differences. First, if example.net hosts the virtual domain virtual.example.com, it's generally not true that messages sent to [e-mail] will end up in the same mailbox as messages sent to [e-mail]. Each virtual domain has its own private namespace, which is also distinct from the namespace of the local system.

With qmail, virtual domains are configured in the virtualdomains file, which consists of one or more entries of the form:

 user@domain:prepend 

qmail converts user@domain to prepend-user@domain and treats the result as if domain was local. The user@ part is optional. If it's omitted, the entry matches all @domain addresses.

Returning to the previous scenario, if the example.net mail administrator wanted to create a virtual domain, virtual.example.com, under the administrative control of user john, the following entry in virtualdomains would accomplish that:

 virtual.example.com:john 

An incoming message to [e-mail] would be rewritten as [e-mail] and delivered locally. See Chapter 4, "Using qmail," for more information about how john can manage his virtual domain.

As with multiple host names, all virtual domains must be listed in rcpthosts so qmail-smtpd will know to accept messages addressed to them. However, unlike multiple host names, virtual domains must not be added to locals.

Remember to send the qmail-send process a HUP signal after modifying virtualdomains to tell it to re-read the file:

 # qmailctl hup Sending HUP signal to qmail-send. # 

Note 

Domain Name System (DNS) mail exchanger (MX) records must be set up to direct messages for virtual domains to the appropriate mail server. This is a job for the name server administrator and is beyond the scope of this book.

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