When using webmail, you may receive the following error message:
Error: SMTP Server rejected email. Returned:503 sender not yet given.
This is very easy to fix, simply follow the instructions below:
1. Login to the affected webmail account.
2. Click on the Preferences option at the top.
3. Click on the Account Preferences option.
4. In the Reply To field, enter a valid email address.
5. Scroll down to the bottom of the page and click on the Save Settings button.
The issue will now be fixed and you will no longer receive the error message.