526 Authentication failure[0] - AuthenticationFailedException

I followed the instructions from this on how to set up the SMTP.

My traccar.xml is as below and I pretty sure that the mail.smtp.host, mail.smtp.port, mail.smtp.ssl.enable, mail.smtp.username, mail.smtp.password, mail.smtp.from paramters are correct.

    <entry key='mail.smtp.host'>smtp.example.com</entry>
    <entry key='mail.smtp.port'>465</entry>
    <entry key='mail.smtp.ssl.enable'>true</entry>
    <entry key='mail.smtp.username'>traccar@example.com</entry>
    <entry key='mail.smtp.password'>GuessWhatisThis</entry>
    <entry key='mail.smtp.from'>traccar@example.com</entry>
    <entry key='mail.smtp.fromName'>Hello World</entry>

But I keep getting the error below:

526 Authentication failure[0] - AuthenticationFailedException (... < SmtpMailManager:154 < *:99 < NotificatorMail:44 < Notificator:39 < NotificationResource:107 < ...)