XCON: Size Limits May Cause Message Looping

• Microsoft Exchange Server, versions 4.0 and 5.0

SYMPTOMS

You have a Microsoft Exchange Server Organization configured with multiple Sites connected by X.400 connectors, and each Site has a Microsoft Mail Connector servicing the same set of Microsoft Mail postoffices. The Microsoft Mail Connectors have a size limit imposed but the X.400 connector does not.

You send a message that exceeds the size limit, but it is a long time, perhaps several hours, before you receive a non-delivery report (NDR).

CAUSE

A message that exceeds the size limit should result in an immediate NDR; however, because the routing table has an alternate route over the X.400 connector to the other site, the message transfer agent (MTA) reroutes the message until it reaches the hard-coded hop count of 512.

A message will go through the 512-hop count before returning an NDR if a particular user is restricted from using all the connectors of a particular type (for example, all IMCs in an organization). A restricted user may not receive an NDR for hours (depending on the Microsoft Exchange Server topology).

This behavior is by design for Microsoft Exchange Server. The Microsoft Exchange Message Transfer Agent (MTA) does not store detailed data about each reroute in the P1 header of each message that passes through the MTA. This could potentially make individual messages much larger because each time they pass through another MTA, the Internal-Trace-Information-Element would significantly grow in size. This could severely degrade MTA performance. The P1 header of a message passing through the MTA only contains destination MTA name, hop count, and routing action information.

WORKAROUND

To work around this problem, do one of the following:

• Have a consistent size limit for the organization. Set this on the MTA object of the server objects.
• Eliminate redundant paths to the same destination. (Have only one Microsoft Mail Connector servicing that set of postoffices).

STATUS

This behavior is by design as stated for Exchange Server.