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Hence,
a standard format known as MIME (Multipurpose Internet Mail Extensions)
has been created to describe the message parts and mail program conforming
to this standard will be able to describe its own messages and interpret
messages created by other systems.
(MIME) Multipurpose
Internet Mail Extensions
MIME
encoded messages consist of many
parts--each part is allowed to be described in detail and some parts
encoded. The purpose of MIME is to describe the many parts of an email
message, such as attached sound files and images.
MIME messages
may include a plain text message and a GIF image--because GIF image is
binary data consisting of 8 bit characters. To get the GIF image data to
pass through the Internet--Base 64 is
used to encode the data into 6-bit characters.
MIME is also
used to annotate part of a message so that the receiving mail reader will
know what data is stored in the message and process it optionally, ie;
instead of listing the GIF file as a generic attachment--may automatically
display it instead.
Message encoding
binary data is often represented by 8 bit characters and some computers on the
Internet are unable to transfer data represented by 8 bit characters.
Therefore, the encoding process must convert 8 bit characters into smaller
characters for sending across the Internet and then re-convert back to 8 bit
characters by the receiving computer.
Base 64, UUencode
and Quoted Printable are the most popular (there are several types
of data encoding). Since many Internet email infrastructure was not designed
to handle email messages containing binary information like file
attachments--they are converted into a format that is compatible with
computers on the Internet and this conversion process is called encoding.
Base 64
is
generally used to encode binary attachments with MIME formatted messages and
transforming 8 bit characters into 6 bit characters--which are compatible with
the Internet infrastructure (will approximately increase data size to 130%)
compared to the original.
UUencode (Unix to
Unix) is an older form of data encoding that transforms 8 bit data
into characters that are compatible with the Internet infrastructure. And most
mail systems that support Base 64 are also
backwards compatible with Uuencode--which can
only be understood by some older mail systems.
Quoted Printable
encoding is suitable when small portions of the message data are stored into 8
bit characters, usually for text message that consists of characters less than
8 bits--normally for the message body text.
Quoted Printable encoding is designed to
transform 8 bit characters into characters compatible with the Internet,
similar to Uuencode or Base
64 -- the difference is that “Quoted Printable” does not convert all
the characters of the message, it only transforms characters which use more
than 7 bits and any 8 bit characters are split into two or three smaller
characters.
Email messages
are text files formatted to specifications outlined in
RFC 821 (Request For Comment)
documents, that describes in detail how messages should be formatted and how
systems should communicate with each other by following these guidelines.
An email message
has the following parts: RFC-822 Message Header and Message Data
RFC-822 Message Header is the first part all email messages, it
specify the many options of the message and includes the subject line and
headers are not required to be placed in any
particular order. A MIME formatted message may
contain many parts and each part may contain its own header and in the message
data section.
Example of a Message Header:
Reply-To: "Service" <service@bouncemailmanager.com>
From: "Tony" <service@bouncemailmanager.com>
To: "Wendy" <support@mailsbroadcast.com>
CC: "CEO" <ceo@mailsbroadcast.com>
Subject: I am getting too many bounce mails.
Date: Mon, 11 Nov 2002 12:38:23 -0400
MIME-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
X-Priority: 1
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2600.0000
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000
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