In order to make full use of the capabilities of Procmail it is worth spending some time to understand the basic structure of a typical e-mail message. Over time, the structure has grown in complexity, but it can still be broken down into two discrete blocks.
The message body is separated from the headers by a single blank line (all the headers must be on consecutive lines as any headers following a blank line will be assumed to be part of the message body).
The message body itself may be either a simple text message composed normally of simple ASCII characters or it may be a complex combination of parts encoded using something known as MIME. This has allowed e-mail to be able to transfer all forms of data ranging from simple text, HTML, or other formatted pages and to include information such as attachments or embedded objects such as images. Discussion of MIME encoding is beyond the scope of this book, and is not necessary for most processes that...