I did a google search and check a few sites and this looked the most 
complete, I hope it helps.

http://www.dsv.su.se/jpalme/ietf/mail-headers/mail-headers.html#Heading6

John Miller

At 05:14 PM 1/25/01 -0600, you wrote:
>How do mail headers grab attachments?  I am writing a script to run in a
>webpage that automatically grabs a log file and emails it.  I want to attach
>it, and send it out.  In php you can write the mail header yourself, and I
>want to try to write the attachment in the header.  Any help would be
>appreciated.
>
>TIA
>
>Brett Astleford
>Platinum Design Group
>
>ps-if you can read headers you'll know I'm using outcrook, sorry...just
>using what my comp gives me :(
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