This document discusses email protocols and security. It describes POP3 and IMAP4 for accessing email on servers, and how MIME allows non-ASCII data to be sent through email by transforming it to ASCII format. It also discusses web-based email services from companies like Hotmail, Yahoo, and Google that provide email through websites. Finally, it mentions that while basic email protocols don't provide security, methods like PGP and SMIME can be used to secure email exchanges.

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Computer Network Administration
Electronic Mail - POP, IMAP, MIME

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 POP3
 IMAP4
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Figure 23.13 Pop3 and IMAP4
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Figure 23.14 Pop3
TCP/IP Protocol Suite 4

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23-5 MIME
Electronic mail has a simple structure. Its simplicity,
however, comes with a price. It can send messages only in
NVT 7-bit ASCII format. In other words, it has some
limitations. Multipurpose Internet Mail Extensions
(MIME) is a supplementary protocol that allows non-
ASCII data to be sent through e-mail. MIME transforms
non-ASCII data at the sender site to NVT ASCII data and
delivers it to the client MTA to be sent through the
Internet. The message at the receiving site is transformed
back to the original data.
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 MIME Headers
TCP/IP Protocol Suite 6

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Figure 23.15 MIME
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Figure 23.16 MIME header
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Figure 23.17 Base64
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Figure 23.18 Quoted printable
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23-6 WEB-BASED MAIL
E-mail is such a common application that some
websites today provide this service to anyone who
accesses the site. Three common sites are Hotmail,
Yahoo, and Google. The idea is very simple. Let us go
through two cases:
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 Case I
 Case II
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Figure 23.19 Web-based e-mail, case 1
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transactions
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Figure 23.20 Web-based e-mail, case 2
HTTP
transactions
HTTP
transactions
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23-6 E-MAIL SECURITY
The protocol discussed in this chapter does not provide
any security provisions per se. However, e-mail
exchanges can be secured using two application-layer
securities designed in particular for e-mail systems.
Two of these protocols, Pretty Good Privacy (PGP)
and Secure MIME (SMIME) are discussed in Chapter
30 after we have discussed the basic network security.
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