Go to gmail.com
Click the settings wheel icon and choose accounts and imports
Under send mail as click Add another email address you own
Enter your name and domain email and leave the box checked
select use your own smtp not the gmail one
enter yourMailServer.com for the server, yourMailUserName for the username and your password. change the port to 25 and use the default security.
enter the verify code that is mailed to your domain email.
In your outlook
outgoing server smtp.gmail.com
requires ssl YES
requires authentication YES
account name - YOUR GMAIL ADDRESS firstname.lastname@example.org
password - gmail password