1/ setup email in your moodle instance 2/ create some users with valid emails 3/ try messaging user - they should get email if not logged in
note: you can use email debugging to get info why it does not send emails
see https://github.com/Synchro/PHPMailer/blob/master/changelog.md
MDL-47299 Upgrade PHPMailer to 5.2.9 for Moodle 2.8 release
MDL-43947 SMTP not working in moodle 2.6
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