This error is usually a result of your email client not correctly authenticating with the mail server. This is only a small issue and can quickly be rectified.
- Make sure you are using your full email address, for example: email@example.com
- Make sure you have enabled the setting "My server requires authentication"
- Double check all settings within email client.
The settings should be as follows:
- Incoming Mail Server - mail.domainname.com
- Outgoing Mail Server - mail.domainname.com
- Username - your full email address
- Make sure "My SMTP server requires authentication" is enabled
If you have any other queries please get in touch with out support team.