Didn’t get an e-mail notification for this reply. Hmmm.
I found out that that plugin requires an Enterprise License of Mattermost, so I disabled it.
As for the was error, my apache config only has ws:// as shown by your apache config above. I took from yours what I needed for my config.
After some digging it seems I needed to have proxy_ajp enabled for Apache.
Mattermost is now auto-updating in the browser when new messages are posted.
Thanks for your help.
Anya advice on how to setup Postfix and configure Mattermost to properly enable e-mail notifications?