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pradeep 21Apr2005 00:10

Why Are Attachments Encoded?
 
Have you ever wondered why e-mail attachments are encoded? Well read ahead tro find the answer to this.

Internet e-mail and Usenet news posts were designed for plain text messages. As such, many systems expect the messages to only contain printable characters from the 7-bit (first bit of the 8-bit byte is always zero) ASCII character set. These programs can have problems if the message includes extended 8-bit (the first bit is a one) characters, such as the various accented letters. This also poses a problem for sending files, such as images, sound, video, spreadsheets and programs which can contain any combination of 8-bit binary data. This even poses a problem for formatted documents, since many word processors embed binary control fields in the files.

The way around this limitation is to encode the binary data (attachment) into ASCII characters before sending. To the mail and news systems that the messages travels through, the file is just so much text. At the receiving end, the message is decoded back into the original file, none-the-worse for the experience. Many mail and news programs automate the encoding and decoding. However, sometimes a separate program may be required.

The nice thing about Standards is there are so many to choose from. Encoding is no exception. Among the more popular are: Uuencode, MIME, Base64, Quoted-Printable, Binhex and yEnc. There are other less common methods as well.

It should be noted that encoding is not the same as encryption. The purpose of encoding is to allow some information to be stored in, or pass through, a medium that can't handle the data directly. The purpose of encryption is prevent unauthorized persons from view or using some information. It's possible for a message to use both encoding and encryption.

More coming soon...about the encoding methods.


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