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Postfix Documentation
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Postfix Address Rewriting


Postfix address rewriting purpose

Address rewriting is at the heart of the Postfix mail system. Postfix rewrites addresses for many different purposes. Some are merely cosmetic, and some are necessary to deliver correctly formatted mail to the correct destination. Examples of address rewriting in Postfix are:

  • Transform an incomplete address into a complete address. For example, transform "username" into "username@example.com", or transform "username@hostname" into "username@hostname.example.com".

  • Replace an address by an equivalent address. For example, replace "username@example.com" by "firstname.lastname@example.com" when sending mail, and do the reverse transformation when receiving mail.

  • Replace an internal address by an external address. For example, replace "username@localdomain.local" by "isp-account@isp.example" when sending mail from a home computer to the Internet.

  • Replace an address by multiple addresses. For example, replace the address of an alias by the addresses listed under that alias.

  • Determine how and where to deliver mail for a specific address. For example, deliver mail for "username@example.com" with the smtp(8) delivery agent, to the hosts that are listed in the DNS as the mail servers for the domain "example.com".

Although Postfix currently has no address rewriting language, it can do surprisingly powerful address manipulation via table lookup. Postfix typically uses lookup tables with fixed strings to map one address to one or multiple addresses, and typically uses regular expressions to map multiple addresses to one or multiple addresses. Fixed-string lookup tables may be in the form of local files, or in the form of NIS, LDAP or SQL databases. The DATABASE_README document gives an introduction to Postfix lookup tables.

Topics covered in this document:

Postfix Documentation
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