In some cases, qmail's built-in virtualization support is insufficient to achieve the desired separation between virtual domains. For example, when using the built-in virtualization features the central queue is shared among all of the virtual domains, as is the qmail-send
process. Because the qmail-send
process is shared, each of the virtual domains will send outbound email from the same IP address and will have to share remote delivery slots. Because the queue is shared among the virtual domains, all domains must use the same queue management policies, such as the queue lifetime setting, the bounce settings, the double-bounce settings, and so forth.
Virtual domains using the built-in virtualization schemes also frequently share an external IP address and thus share a qmail-smtpd
server. This forces all the virtual domains to use the same receiving policies as well, such as which (if any) blacklists to use or whether to do SMTP tarpitting or...