Setting up your server to send and receive e-mails
To handle e-mail, your server needs to run a service called a Mail Transfer Agent (MTA) that is capable of:
Receiving incoming e-mail and placing it in the user's local mail spool
Sending e-mail to other MTAs for delivery to users on remote systems
MTAs exchange messages using Simple Mail Transfer Protocol (SMTP). A mail server listens for connections on port 25 and accepts incoming e-mail messages from anywhere on the Internet. If the message is addressed to a valid local address, it should be delivered to the destination mailbox.
When a user of our server decides to send an e-mail, the MTA picks up the message, checks where it is addressed to, and forwards it to the MTA associated with the destination domain.
Note
MTAs can also relay e-mails—forward e-mails coming in over SMTP but bound for other destinations. This is discussed in the Setting up a secure SMTP relay for users recipe later in this chapter.
In this recipe, we will set up the Postfix...
