When you try to send email using Microsoft Outlook, Windows Mail, macOS Mail, or other email client software, you may receive the message stating that “550 Authentication is required” from your mail server.

The cause for this error is that your email server is configured to require SMTP authentication to send outgoing emails, which is a way an email sender can be authorized. In order to resolve this error, you will need to configure your email
client (Outlook, Outlook Express, macOS Mail , Thunderbird, etc.) to send the appropriate credentials.

SMTP Authentication in Microsoft Outlook 2010 for Windows

1. Click on File then hover over Info and click on Account Settings.
2. Select your email address from the list of accounts and click Change.
3. Click on More Settings…. Then click on the Outgoing Server tab.
4. Check the box next to My outgoing server (SMTP) requires authentication and ensure the Use same settings as my incoming mail server is selected.
5. Click OK. Then click Next.
6. Click Finish to complete the configuration.

SMTP Authentication in Microsoft Outlook 2003

1. Click on the Tools menu and select Email Accounts.
2. Select View or change existing e-mail accounts and click Next.
3. Select your email address from the list of accounts and click Change.
4. Click on More Settings. Then click on the Outgoing Server tab.
5. Check the box next to My outgoing server (SMTP) requires authentication and ensure the Use same settings as my incoming mail server is selected.
6. Click OK. Then click Next.
7. Click Finish to complete the configuration.

SMTP Authentication in Microsoft Outlook Express

1. Click the Tools menu in Outlook Express.
2. Click Accounts.
3. Highlight an email account and click Properties.
4. Click the Server tab.
5. Under the Outgoing Mail Server, check the “My server requires authentication” check box.
6. Click the Settings button.
7. Make sure that “Use same setting as my incoming mail server‘ is selected.
8. Click OK.
9. Click Apply.
10. Click OK.
11. Click Close.

SMTP Authentication in Mail for macOS

1. Mail.app > Mail > Preferences.
2. Select Accounts > Account Info.
3. Select the Outgoing Mail Server (SMTP) field and pick Edit Server Lisr from the pop-up.
4. Select one of the SMTP Servers or add new one.
5. Select Advanced.
6. Select Password Authentication, and use TCP Port 465, and select SSL/TLS connection security.
7. Enter your outgoing sever, email address and password for the SMTP Server.
8. Save and exit.