NOTE: Pls enable IMAP/POP in Google Apps Email setting first before doing the below step, read here for more info
If IMAP is not enabled the below settings will not work

1. Open Outlook.
2. Click Files in the navigation bar, and select Add Account

3. On the E-mail tab, click New…
4. If you are prompted to Choose E-mail Service, select Microsoft ExchangePOP3, IMAP, orHTTP, and click Next.
5. Enter your display name, email address (including ‘@gmail.com’), and password. Google Apps users, enter your full email address, e.g. ‘username@your_domain.com.’
6. Select the ‘Manually configure server settings or additional server types‘ checkbox.

7. Select Internet E-mail.
8. Settings: name, full email address (including ‘@gmail.com’ or ‘@your_domain.com’)
-In the Account Type dropdown menu, select IMAP. In the ‘Incoming server name’ section, enter: imap.gmail.com and in the ‘Outgoing server name (SMTP)’ section, enter: smtp.gmail.com.
-In the ‘User Name’ field, give your full Gmail address, including ‘@gmail.com’ or ‘@your_domain.com.’
-After creating these settings, clicking More Settings.

9. Select the Advanced tab.
-Incoming server must be 993, and must use SSL encryption.
-Outgoing server can use 587, TLS encryption.

10. Click the Outgoing Server tab. Make sure that ‘My outgoing server (SMTP) requires authentication’ is selected. The radio button ‘Use same settings as my incoming mail server’ should also be selected.

11. Click OK, then click Next. After test is completed, hit Close, and Finish.