RFC 2789 (rfc2789) - Page 3 of 33

Mail Monitoring MIB

RFC 2789                  Mail Monitoring MIB                 March 2000


2.  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 is
   modelled as occurring 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) If necessary messages are converted into the format that's
       appropriate for the next hop. Conversion operations may be
       successful or unsuccessful.

   (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.

3.  MTA Objects

   If there are one or more MTAs on the host, the following MIB may be
   used to monitor them. Any number of the MTAs on a single host or
   group of hosts may be monitored. Each MTA is dealt with as a separate
   network service 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 RFC 2788 [16].




Freed & Kille               Standards Track