Problem:
When attempting to send email using Microsoft Outlook, Outlook Express, or other email client software, you may receive the message "550 Authentication is required for relay" from your mail server.

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

Resolution:
To solve this problem, configure your email client to use SMTP authentication.  Instructions for a few email clients are shown below. The exact steps to use, however, depend on the version of software you use, so the instructions below are provided as a reference and are intended to get you headed in the right direction.

For Microsoft Outlook, do the following:

1. Click the Tools menu in Outlook.
2. Click Email Accounts.
3. Click View or change existing e-mail accounts.
4. Click Next.
5. Highlight an email account.
6. Click Change.
7. Click More Settings.
8. Click Outgoing Server tab.
9. Check the My outgoing server (SMTP) requires authentication.
10. Make sure that Use same setting as my incoming mail server is selected.
11. Click OK.
12. Click Next.
13. Click Finish.

For Outlook Express, do the following:

1. Click the Tools menu in Outlook Express.
2. Click Accounts.
3. Hightlight 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.