Unpropagating a message might also be known as removing an alert or removing an alert from the latest alerts feed.
When you propagate a message, this will send out a tweet about it, post it on the latest alerts feed on your associations alert website and create a web page for it. Unfortunately, when unpropagating a message that you no longer wish to be public, it is not possible to stop anybody who received it directly (not viewing it online) from continuing to view it as they have a copy of it. It is only possible to stop people from reading the message online.
To unpropagate a message, you will need to first of all ensure you are logged into your administrator account and are able to see a screen that looks like this:
Next, on the left hand side open up "Communications", and then "Message History".
You will then need to locate your message by message number or subject.
Once you have located the message, click the "eye" icon underneath the message heading next to the correct message. This will open up a page which contains the message.
You wiill notice on the screenshot above "Tick this box to display this alert in the latest alerts section of the website" is ticked. This means that the alert has been propagated. To unpropagate it, simply untick the box. This means that whenever anybody tries to view the message in their web browser, it will give them a message telling them that it is not available to view.