Unable to send email from OC 8.1.5 from OTP Users app

[DFWJim]

When going into the OTP Users app on the left side of OC community 8.1.5, clicking email does nothing. Reviewing the owncloud.log file, it shows this:

...."app":"PHP","message":"Class 'OC_Mail' not found at /var/www/html/owncloud/apps/user_otp/ajax/personalSettings.php#97","level":3,"time":"2016-01-09T10:03:28+00:00"}