The issue you are facing is due to the password inserted for the email address in the email client is incorrect. If you are getting the following error that was in the screenshot below, then please follow the following.
In your email client check the login details inserted by you. Please insert the password again for that email account and then check.
If you still face the same issue then we would recommend you to check your login details by accessing webmail in the web browser.The webmail URL will be "http://webmail.yourdomain.com " and if you are not able to login to that then you need to update your mail server administrator to reset your email account password.
You may refer the following link if you want to check where to insert the password again for the email client you are using.