If you're getting this error when sending out email.
Please double check your email setting to use the following
For Microsoft Outlook
1. Click Tools then E-mail Accounts...
2. Select "View or change existing e-mail accounts" and click Next
3. Select the email account and click Change
4. Click on "More settings"
5. Select "Outgoing Server" tab
6. Tick "My outgoing server (SMTP) requires authentication"
7. Select "Log onto incoming mail server before sending"
8. Click Ok
9. Press Next
10. Lastly, press Finish
Once these steps are done, try to send the reply email again.