Why do list members get multiple copies of a list posting?

Question

Some list members complain that they get more than one copy of a message. What can cause this?

Answer

There are several reasons why messages to lists can be duplicated with are nothing to do with the way that GMS Communication Server operates. Many are transitory and some are permanent. Some are listed below:

1. Duplicate postings. If a list member posts their message to the list twice, it will be delivered twice and all the list members will get two copies. This is likely to be a transitory repeat.
2. Duplicated by mail servers. As the message travels to GMS Communication Server and then on to each list member, it passes through many mail servers. Any of those mail servers may duplicate the message. If the message is duplicated before it arrives at GMS Communication Server, every member of the list will get an additional copy.
3. More than one email address. Some list members may have several email addresses and added several of them to the list. In this case, one list member will be affected and they will always get two (or more) copies of each message. To resolve this, remove the additional email addresses from the membership list.

Investigation of which error has occured starts with the headers of the recipient’s messages. Comparing the two will often show where the message was duplicated so that appropriate action can be taken.

To help reduce multiple posts from users, you can use Post Moderation on your lists, this way only messages that are accepted are posted to the list. It is up to the moderator to identify the duplication of messages and only accept one of them.

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