- Enable debug in the felix console at http://localhost:4502/system/console/configMgr/com.day.cq.mailer.DefaultMailService
- Check the stdout.log Or stderr.log it will provide exact reason for failure.
- The common mistake I hear about this is either missing from field Or ssl over smtp enabled/disabled at mail service config.
I hope this would help you.
Thanks and Regards
Kautuk Sahni