PC Ext: Increasing Retry Count for LAN-Based Mail (119884)

SUMMARY

It is possible to set retries for each external postoffice defined on a network. This might be desirable when frequent "retry count exceeded" messages are displayed in the SYSTEM.LOG file. The ADMIN.EXE program directly supports setting the retries for postoffices with routing defined as Direct via Modem. Once this count has been set, it is retained when the postoffice routing is modified to Direct via MS-DOS drive.

To set the retry count for mail destined to a specific postoffice:

Run ADMIN.EXE at the postoffice that is the source of the mail.
Select External-Admin, Modify and choose the destination network name and postoffice.
Specify routing to be Direct via Modem.
Answer yes to the Modify? prompt.
Select External-Admin, Setup and press <ENTER> at the network name.
Select the Options and Retries menu item.
Enter the desired number of Retries for the postoffice. Escape back and select Yes to update the record.
Select External-Admin, Modify and change the routing of this postoffice back to its former routing, such as Direct via MS-DOS Drive.
Answer yes to modify the postoffice.

This will have reset the count in the XTN file.

NOTE: This change does not immediately become effective. The External program, which makes use of this count, caches this information in memory and will not have the new value until it updates from the postoffice.

Updating occurs when External starts and when the update interval is reached. The update interval is normally five minutes, but it can be set to a different value through command line and INI settings using the IntervalUpdate= parameter. See Chapter 12 of the "Administrator's Guide" for more information on External parameters.

MORE INFORMATION

How the Retry Count is Used

External will cycle through the queues of external postoffices looking for mail to be dispatched. If mail is to be transferred and an attempt to deliver this mail is unsuccessful, External will update the queue to reflect that an additional retry occurred. Each time an error occurs on a specific mail item, its retry count is incremented. After incrementing, the number is compared to the maximum retry count associated with the destination postoffice. If the number is equal to or exceeds the retry count, the mail is considered undeliverable and will be returned to the originator.

The default retry count for a mail item is 3. This means that after 3 attempts, the item is returned and the following message is placed into the SYSTEM.LOG:

[005] Mail Retry count exceeded sending to: ...

How Changing the Retry Count Effects Mail Delivery

When there is only one MTA (External) processing mail at a postoffice, the span of time before a mail item is returned would generally be about 15 minutes. This is based on a retry count of 3 and an interval of 5 minutes between MTA cycles. If External cannot make a full cycle of all postoffices in 5 minutes, the total time could be longer. This 15 minutes might be long enough for temporary network problems to be eliminated and for the item to successfully transfer.

When multiple MTAs operate in a mail configuration, the span of time before the retry count is exceeded is difficult to predict. Consider a situation in which three MTAs operate. It is possible that one MTA would have just finished updating the retry count for a mail item and another MTA would make another attempt. If all three MTAs were close behind one another, then the default retry count could be exceeded in a matter of a few minutes. In this case, updating the retry count could provide a needed time buffer.

The best scenario is one in which the network, routers, and servers rarely fail. If at all possible, steps should be taken to remedy problems in these areas rather than have excessive retries.

The Retry Count Effects Notification of Mail Problems

If External is persistent (high retry count) in its attempt to deliver mail, mail can sit in queues for a long time before the sender is notified that there is a delivery problem. As explained above, this is dependent on the number of MTAs operating and the cycle interval.

NOTE: Until the retry count is exceeded, the sender has no indication that there are delivery problems. For the known unreliable network connections, the administrator is faced with the task of balancing the competing priorities of persistent mail delivery vs. the senders need to know that his mail has not yet been delivered.