virtusertable

virtusertable is a configuration file used by sendmail and other Mail Transfer Agents (MTAs) for virtual hosting. It allows a single mail server to handle email for multiple distinct domains, even if those domains do not have their own physical mail servers. The virtusertable maps incoming email addresses to different local or remote destinations.

The basic format of a virtusertable entry is simple: the left side specifies the recipient email address, and the right side specifies the destination for that email. For example, an entry like "[email protected] [email protected]" would redirect all mail sent to [email protected] to [email protected]. The destination can be a local user on the same server, another mailbox on a different server, or even a program to process the mail.

There are several common uses for virtusertable. It's frequently employed for domain aliasing, where multiple domains all deliver mail to the same set of users. It's also used to consolidate mail for many small domains onto a single server, simplifying administration. Furthermore, it can be used to redirect mail for deleted or renamed accounts to a new address.

The virtusertable is typically read by the sendmail lookup table mechanism. After modification, the table needs to be recompiled into a database format, usually with the `makemap` command, for the MTA to recognize the changes. This mechanism provides a flexible way to manage email delivery for virtual domains without requiring separate mail servers for each.