List Library - Message Deduplication

This document describes how the List Library handles duplicate messages.

Definitions

List Library Configuration

The List Library lists are configured as follows:

These settings result in the following email list behavior:

All of these settings only apply to messages sent in the last 24 hours. Also note that these settings will not apply to a message that is sent to multiple lists at the same time, i.e. multiple list addresses in the to field. The List Library must process each message separately to know to which lists and which members it has been sent.

Examples

  1. Mary creates a message and addresses it to uwofficial-all@lists.wisc.edu and uwofficial-colleges@lists.wisc.edu. The message goes to both lists. If Bob is on both email lists, he will get the message twice.
  2. Mary creates a message and addresses it to uwofficial-all@lists.wisc.edu, waits 5 minutes, and then sends it to uwofficial-colleges@lists.wisc.edu. The message goes to both lists. If Bob is on both email lists, he will only get the message once because the List Library knows he already got the message from uwofficial-all@lists.wisc.edu.
  3. Mary creates a message and addresses it to uwofficial-all@lists.wisc.edu. There is a lot of traffic that day and Mary doesn’t get a copy of her message right away, so she sends the same message to uwofficial-all@lists.wisc.edu again. Only one message goes out, and the second is rejected as a duplicate.