The following are the common causes of the error:
- The account is over-quota. The space allocated to the account is full.
- Your email client isn’t set up for SMTP Authentication.
The account is Over-quota:
If the account has been working seamlessly then suddenly brings the error, this is normally the cause. If this is the case, contact the server administrator or hosting provider to increase your hosting space.
Setting up SMTP Authentication:
- Open the Tools/ Files menu and select Account Settings.
- Double-click on the affected email account.
- Click on More settings
- Click on the Outgoing Server Tab.
- Enable My outgoing server (SMTP) requires authentication then retain the rest of the settings as they are.
- Click OK to save your settings.