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Postfix: The Definitive Guide by Kyle D. Dent

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Chapter 7. Local Delivery and POP/IMAP

Chapter 1 explained that POP and IMAP are protocols that deal with how users retrieve their email messages from message stores. Postfix is a mail transfer agent and does not implement POP or IMAP. This chapter looks at how Postfix delivers messages and how they are read by POP/IMAP servers. There are many POP/IMAP servers available, and the information presented here should be applicable to any standards-conforming server. The last part of this chapter deals with configuring Postfix to work with the Cyrus IMAP server. Before we look at local delivery, we'll first discuss more broadly the different delivery transports Postfix uses. Transports other than local are discussed in subsequent chapters.

Postfix Delivery Transports

Postfix offers delivery for four different classes of recipient addresses: local, relay, virtual alias, and virtual mailbox. How you configure the domains you accept mail for determines the delivery method used by Postfix. The following are the delivery transports used by Postfix:

local

Delivers mail on the local system. Each address has an account on the system or comes from the local aliases file (historically /etc/aliases). Delivered messages go to the system's mail spool or mail files in individual home directories. Deliveries are handled by the local delivery agent or passed to a custom delivery program. Lists local domains in the mydestination parameter.

relay

Delivers mail to other systems, usually on the same network. ...

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