Sun Internet Mail Server 3.5 Reference Manual: 3

Message Structure

Most IMTA messages are stored as text files. Messages with multiple parts (possibly containing different types of data) are represented as a series of text sections separated by special unique delimiter strings.
A sample mail message file is given below.
m;DAN@SIGURD.COMPANY.COM  (1)
ned@YMIR.UNIVERSITY.EDU 
(2)
Received: from SIGURD.COMPANY.COM by SIGURD.COMPANY.COM (IMTA 
#11000) id 
<01G6YTYFU6748WWH0Y@SIGURD.COMPANY.COM>; Thu, 13 Jun 1991 15:01 
PDT 
Date: Thu, 13 Jun 1991 15:01 PDT 
From: "Daniel C. Newman" <DAN@SIGURD.COMPANY.COM> 
Subject: Mrochek ate my shoe 
To: ned@YMIR.UNIVERSITY.EDU 
Message-id: <01G6YTYFU6748WWH0Y@SIGURD.COMPANY.COM> 
MIME-version: 1.0 
Content-type: TEXT/PLAIN; CHARSET=US-ASCII 
Content-transfer-encoding: 7BIT 
X-Envelope-to: ned@YMIR.UNIVERSITY.EDU 
X-VMS-To: IN%"ned@ymir.university.edu" 
(3)
Ned, 
Mrochek ate another shoe of mine....

Dan

(4)
(5)
Briefly, the key items in each message file are:

	1.	The message envelope. The first records in the file contains message envelope (i.e., transport) information. The envelope is terminated by a record containing to two CTRL/A characters.
	2.	The header lines of the message follow the envelope; their format is mandated by RFC 822.
	3.	There may be any number of message header lines; the message header formed by this collection of header lines is terminated by a single blank line after which follows the message body.
	4.	The message is terminated by a sequence of five CTRL/As.
	5.	For messages that had transient delivery failures, information about retrial would go here.

Note - Sun reserves the right to change this format in future releases of the IMTA. User-written applications that either read or write queued IMTA message files should make use of appropriate IMTA library routines. Use of the IMTA SDK will insulate user applications from any future message format changes.