RFC 1566 (rfc1566) - Page 3 of 20

Mail Monitoring MIB

RFC 1566                  Mail Monitoring MIB               January 1994


3.  Message Flow Model

   A general model of message flow inside an MTA has to be presented
   before a MIB can be described. Generally speaking, message flow
   occurs in four steps:

   (1)  Messages are received by the MTA from User Agents, Message
        Stores, other MTAs, and gateways.

   (2)  The "next hop" for the each message is determined. This is
        simply the destination the message is to be transmitted to;
        it may or may not be the final destination of the message.
        Multiple "next hops" may exist for a single message (as a
        result of either having multiple recipients or distribution
        list expansion); this may make it necessary to duplicate
        messages.

   (3)  Messages are converted into the format that's appropriate
        for the next hop.

   (4)  Messages are transmitted to the appropriate destination,
        which may be a User Agent, Message Store, another MTA, or
        gateway.

   Storage of messages in the MTA occurs at some point during this
   process. However, it is important to note that storage may occur at
   different and possibly even multiple points during this process. For
   example, some MTAs expand messages into multiple copies as they are
   received. In this case (1), (2), and (3) may all occur prior to
   storage.  Other MTAs store messages precisely as they are received
   and perform all expansions and conversions during retransmission
   processing. So here only (1) occurs prior to storage.  This leads to
   situations where, in general, a measurement of messages received may
   not equal a measurement of messages in store, or a measurement of
   messages stored may not equal a measurement of messages
   retransmitted, or both.

4.  MTA Objects

   If there are one or more MTAs on the host, the following mta group
   may be used to monitor them. Any number of the MTAs on a host may be
   monitored. Each MTA is dealt with as a separate application and has
   its own applTable entry in the Network Services Monitoring MIB.

   The MIB described in this document covers only the portion which is
   specific to the monitoring of MTAs. The network service related part
   of the MIB is covered in a separate document [5].




Kille & Freed