Hi,
The football pool plugin has no notification options or method of communication (e.g. mailing list) built in.
You could build something as an extension to the plugin, but my first thought is that it will be a lot of work for something that can also be handled by another plugin and some manual work. So, I don’t immediately see the real benefit of adding it as a functionality on top of the pool.
If you search for a plugin that has mailing list options, or integration with mailchimp or so, you could create a mail template and send out a newsletter when one or more matches are postponed. And in that mail give some information about the consequences for the competition you are running. If there are consequences, that is, because if there are no consequences (e.g. change in monthly ranking with prices), then for the user it will just be information that they get more time to enter/update their predictions.
