Click TOOLS, then E-Mail Accounts

Choose View or change existing e-mail accounts, click Next

Highlight the email address you want to change and click Change

Enter your ISP's outgoing mail server un the "Outgoing mail server (SMTP)" field.

Click More Settings.....

Put a check in My putgoing server (SMTP) requires authentication

Also tick Log on using and enter the user name and password for your ISP account.

Check Remember password.

Click OK

Click ok.

In the open window click Next, then Finish.

That should be it, your outgoing mail server should now be set up.