Dial tone portability is an Exchange feature that enables limited business continuity for failure scenarios where a database, server, or the entire site is affected. It provides users with a temporary mailbox, allowing them to send and receive e-mails while their original mailbox is in the process of being restored. This temporary mailbox can either be on the same Mailbox server or on any other Mailbox server in the organization (as long as it contains databases with an identical schema version), allowing users' mailboxes that were previously on the failed server to be hosted on an alternative server. Clients who support Autodiscover will then automatically be redirected to the new server without the need to manually update the user's profile. Once the user's original mailbox has been restored, the recovered mailbox and the dial tone mailbox can be merged into a single and up-to-date mailbox.

Using dial tone portability is a process called dial tone recovery.

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