Since we were offered a shared Discourse Forum hosting service, our messages are sent from servers that blast out a high volume of mass eMailings.
So at least one free eMail host (Yahoo!) has permanently tagged them as SPAMmers. They bounce mass eMails from those Discourse servers. If you are using a Yahoo eMail address, although individual notifications come through, you will not see “Mailing List Mode” notifications.
Muting a Category in Mailing List Mode
The forum is fairly active. You can mute categories that are not of interest.