Encoded files
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Encoded files

Encoding involves changing data from eight-bit to seven-bit to enable it to travel over the SMTP channel, which was historically a seven-bit only channel. This state of affairs arose because initial designs only concerned themselves with text transfers using restricted ANSI character sets, which failed to consider non-English language characters or file-based attachments.

Therefore, non-seven-bit data has to be encoded into a seven-bit data stream. UUE, which has many variants, and BINHEX are fairly old techniques, and MIME is the current favourite encoding format. If you are looking at content solutions, you should ensure that multi-part UUE and XXE variants are supported.

Encoding is found in binary streams, generally to denote how the data should be treated at the remote end. In HTTP for example, headers will declare the data type of the following transmission. This will tell the browser how to render the data, such as plain text or HTML.

from Content Technologies' Guide to Content Security, 2nd Ed