Choose Accounts from the Tools Menu.
Select your existing email account and click "Properties" or Add
Your General tab settings should at least have your name and your email address.
Now select the Servers tab and it should look like this.
Under Server Information replace "yourdomain.com" with your actual domain name.
Your Account Name should be your complete email address. Be sure to check the box for "My server requires authentication" then click "Settings".
Select "Use
Click on the Advanced tab and set the Outgoing Mail Server Port Number to 587.
That's it.