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Ubuntu Unleashed 2013 Edition: Covering 12.10 and 13.04, Eighth Edition by Matthew Helmke

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How Email Is Sent and Received

Email is transmitted as plain text across networks around the world using the Simple Mail Transfer Protocol (SMTP). As the name implies, the protocol itself is fairly basic, and it has been extended to add further authentication and error reporting/messaging to satisfy the growing demands of modern email. Mail transfer agents (MTAs) work in the background transferring email from server to server, allowing emails to be sent all over the world. You might have come across such MTA software such as Sendmail, Postfix, Fetchmail, Exim, or Qmail.

SMTP allows each computer that the email passes through to forward it in the right direction to the final destination. When you consider the millions of email servers across ...

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