Note: You'll be testing this on Moodle 3.5 AND Moodle 3.6. Make sure you are running either PHP 7.1 or 7.2. As the admin user, run the local jabber server ( https://hub.docker.com/r/rroemhild/ejabberd ) configured with 2 users, and no TLS. docker run --name "ejabberd" \ -p 5222 : 5222 \ -p 5269 : 5269 \ -p 5280 : 5280 \ -h 'xmpp.localhost' \ -e "XMPP_DOMAIN=localhost" \ -e "EJABBERD_ADMINS=admin@localhost admin2@localhost" \ -e "EJABBERD_USERS=admin@localhost:password1234 admin2@localhost:password4321" \ -e "TZ=Europe/Berlin" \ -e "EJABBERD_STARTTLS=false" rroemhild/ejabberd In Moodle, enable Jabber and configure the server details. Set: host: 'localhost' Jabber server: NOT SET For the username, use admin:password1234. Via 'Default message outputs' (search in admin settings for this), enable Jabber for offline AND online use for the 'Personal messages between users' row. Make sure the select is set to 'Permitted'. Create a course and enrol 2 students, student 1 and student 2. Log out. Log in as student 1. Click the notifications bell, and selected preferences (the cog). Click the cog next to Jabber int he column header. Enter 'admin2@localhost' and hit enter to link that user to student 1 Open messaging pane and click the cog (If you're testing on 3.5, just open message preferences and make sure Jabber is on for both online and offline and skip the next step) Enable Jabber output (toggle to on) but leave email and other outputs disabled (we don't want these to interfere for now) Log out. Download pidgin (sudo apt-get install pidgin) Open pidgin and login using student 1's linked jabber account: admin2@localhost with pw: 'password4321' In pidgin account settings (manage accounts -> modify): Under the 'Advanced' tab, set 'connection security' to 'use encryption if enabled' Under the 'Proxy' tab, set 'proxy' to 'No proxy' Leave Pidgin open Now, log in to moodle as student 2 Open messaging, search for student 1 and send them a message. Verify the message is sent in Moodle's UI without any error/debug popups Verify you get a message in Pidgin with the message details.