SMTP

SMTP is used to transfer email across IP network. Here is how the email is transferred.

1.       Email is submitted by a mail client to a mail server using SMTP on TCP port 587 or 25.

2.       MSA delivers the mail to its mail transfer agent.

3.       The boundary MTA has to locate the target host. It uses the DNS to look up the mail exchanger record (MX record) for the recipient's domain.

4.       The MTA next connects to the exchange server as an SMTP client.

5.       MX target accepts the incoming message, and hands it to a mail delivery agent (MDA) for local mail delivery.

6.       MDA deliver messages to storage, or forward them over a network.

7.       On local mail server, the mail is stored for retrieval by mail clients (MUAs).

8.       Mail is retrieved by email clients, using IMAP or POP.