Email Protocols : SMTP, MIME, POP & IMAP


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Table of Contents

Email Protocols : SMTP, MIME, POP & IMAP

‘Email’ means different things to different people

A Typical Mail Environment

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How Email Really Works

SMTP looks exactly like this

The Commands are Few and Specific

SMTP Reply Codes

Reply Codes Contain a Lot of Information

Most Common Reply Codes

RFC821 Defines all the Reply Codes

How to Forge Email

... and the resultant raw mail


Beware of vrfy on some mailers!

SMTP Extensions (EHLO)

An EHLO with Extensions

EHLO with an Old Mailer

Defined SMTP Extensions

SMTP Protocol Key Concepts

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A Typical Mail Message

A Typical Mail Message (continued)

Some Headers are More Important than Others

Anatomy of a Mail Message

Originator Headers: who it comes from

Originator Headers: who sent it on to you

Originator Headers: best reply address

Date Header is Required

Recipient Headers

The Crucial Received Header

Received Lines are Key to What’s Going On

Received Headers Show You the Path

Hop by Hop You Can Follow Each Email Message

Received Line Information

Received Line IP Address Authentication

The Crucial Message-ID Field

Received Headers often contain the Message-ID

Mail Messages Can Get Repeated Several Ways

Header Usage by Mailing Lists

Headers Key Concepts

MIME Multipurpose Internet Mail Extensions

MIME What is it?

MIME Does Two Main Things

How MIME Works

MIME adds new headers

New MIME headers

A sample message with binary attachment

The same boundary marker separates each section

The Content-Type Header

A Minimal MIME Message

Content-Type: Application

Content-type: Multipart

Multipart Messages Can Be Nested

Encoding Schemes are Defined

A Common Sight

MIME Handles Other Character Sets

MIME and Non-capable Mailers?

MIME User Agents

Best Way to Keep on Top of MIME is With the FAQ


... and more MIME RFCs ...

Client / Server Email POP and IMAP

Client/Server Email Follows 3 Main Models

POP and IMAP only get the mail

POP - Post Office Protocol

POP is very simple

POP has no security

IMAP Has Everything POP Doesn’t

In IMAP the Client is King

IMAP Has Stronger Authentication


Use EXAMINE for Debugging

Header Details Can be Seen

See What Folders Are Available

Rummage around in one...

And How To Get Out ...

IMAP Is Everything Needed

Configuring IMAP Service

IMAP Goes Beyond POP

PPT Slide

RFCs of Interest Just a Sample

More Fun RFCs

A Good Place to Get RFCs

Newsgroups of Interest

Author: jms


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