RFC 1566 (rfc1566) - Page 3 of 20
Mail Monitoring MIB
Alternative Format: Original Text Document
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