Nabble itself does not offer a PM system, although it is possible to add in various external resources that may provide what you want. (Try a search for PM in this forum for some suggestions and NAML code to implement them.)
However, for most Nabble users such a system is completely unnecessary as it is always possible to contact any other user privately. You just click on their avatar and get taken to their Profile screen from where there is a link to email that person. If any of your users insist on complete anonymity all they need to do is register with an email address that they use only on the forum.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.
Locked
