OK. Now cron is running, you must look at its output - raising the debug level if necessary. See https://docs.moodle.org/310/en/Cron#Debugging_Scheduled_Tasks.
And on the receiving end you should look at the logs of the SMTP server Moodle is delivering its outgoing mail to.
And on the receiving end you should look at the logs of the SMTP server Moodle is delivering its outgoing mail to.