If the ‘550 SMTP Auth is required for relay’ error message occurs, refer to the simple troubleshooting instructions given here to resolve it.This problem happens when your email server requires the SMTP authentication.
Windows Outlook 2013:
Open the main window of the Microsoft Outlook 2013 application on your Windows computer.
Click the File option, followed by the Info option, and then select the Account Settings option to the 550 SMTP Auth is required.
Now, you will see the email accounts configured in the Microsoft Outlook 2013 email client.
Select the problematic email account and click the Change option.
Click the More Settings button, go to the Outgoing Server tab, and select the checkbox next to the ‘My outgoing server (SMTP) requires authentication’ option.
Check if you have selected the checkbox beside the Use Same settings as my incoming mail server’ option.
Click the OK option, followed by the Next option.
Finish the configuration settings by clicking the Finish option.
Microsoft Outlook 2003:
Go to the main window of the Microsoft Outlook 2003 application, navigate to the Tools menu, and click the Email Accounts option.
Once you select the ‘View or change existing email accounts’ option, click the Next option to get the 550 SMTP Auth is required.
Choose your email account from the Accounts list and click the Change button, followed by the More Settings button.
Now, go to the Outgoing Server tab and select both the options that are given here.
My outgoing server (SMTP) requires authentication
Use the same settings as my incoming mail server
Select OK -> Next -> Finish.
Microsoft Outlook Express:
On the main interface of the Microsoft Outlook Express application, go to the Tools menu and choose the Accounts option.
Click the Mail tab, choose your email account, and select the Properties option.
Click the Servers tab, go to the Outgoing Mail Server section, and select the ‘My server requires authentication’ option.
Once you click the Settings button, select the ‘Use same setting as my incoming mail server’ option.
Click the following options to complete the 550 SMTP Auth is required process.