To enable SMTP Authentication in Microsoft Outlook please follow the followinig steps :-

1) Open Outlook.

2) Select "E-mail Accounts" from the "Tools menu".

3) Select "View or change existing e-mail accounts" .

4) Click Next.

5) Click on "Email account" and click the "Change button".

6) Click on the  "More Settings button ".

7) Click the "Outgoing Server "tab.

8) Place a check in "My outgoing server (SMTP) requires authentication" checkbox.

9) Select "Log on using" and enter your email address in the Username feild and your

password into the Password field OR if you use your same email address for the

incoming mails also (POP3/IMAP) then select "Use same settings as my incoming

mail  server".

10) Click OK, and then click the Next button.

11) Click Finish.