I get a 550 Authentication is required for relay. Print

When you try to send e-mail through your mail client (such as Microsoft Outlook), you get a "550 Authentication is required for relay" message. This is due to the fact our mail server requires you to authenticate yourself first with your e-mail address and password before you can send mail.  This is a measure we have put it effect to prevent unauthorized people from sending mail through our mail server. Therefore, you must enable "SMTP authentication" in your mail client before sending mail.

To enable SMTP authentication in Microsoft Outlook 2000 or greater:

1. Open Microsoft Outlook
2. Click the "Tools" menu
3. Click the "E-Mail Accounts" menu item
4. Choose "View or change existing e-mail accounts" and click Next
5. Select your mailbox from the list of E-Mail accounts and click "Change"
6. Click the "More Settings" button.
7. Choose the "Outgoing Server" tab
8. Check the box titled "My outgoing server (SMTP) requires authentication" and select the "Use same settings as my incoming mail server" option.
9. Click OK to save the settings, then click the OK button to exit the menu                                                                           
   Note: (Click Next instead of OK to continue the account setup for another account)

Now your mail client with authenticate correctly to our mail server and you will be able to send mail.

References:

If you have a mail client other than Outlook, please consult your mail client's help pages for more information on how to enable SMTP Authentication.