Problem Solving: How to Eliminate Duplicate Messages on DBMS Mailing Lists

By Jacob Haller
Senior Support Engineer, L-Soft

Problem

Multiple copies of email messages are posted to your mailing list

Solution

Ask your database administrator to delete duplicate row

When and Why

Mailing lists can be configured to store their subscriber data in an external database. Often, the table the subscriber data is stored in is updated by something other than LISTSERV. This is one of the common reasons people use DBMS mailing lists, to allow them to be easily updated externally.

The problem of duplicate messages arises when the table is updated (by something other than LISTSERV) and results in multiple rows with the same email address. When this happens, it can have some baffling consequences.

A Typical Scenario

1. Subscribers report that they are getting multiple copies of messages posted to the mailing list

2. The list owner checks the subscriber list, finds the duplicate entries and tries to remove one of them

3. LISTSERV sends a command to the database, telling it to set the OPTIONS column for rows containing that email address to NULL. The result is that both duplicate addresses are unsubscribed from the mailing list

4. The list owner observes that the subscriber is no longer subscribed to the mailing list at all and tries to add them back

5. LISTSERV sends a command to the database telling it to set the OPTIONS column for the rows containing that email address to whatever the default for that mailing list is. This results in both of the original duplicate subscriptions being restored.

This is usually when L-Soft technical support receives a support inquiry from a customer organization facing the above scenario. In this case, because the problem is outside of LISTSERV, the solution is for the customer to contact their database administrator and ask them to remove the duplicate row manually.

Next Steps