There are 2 Options depending on the email client you want to use :
Option 1 : Using Google Mail with Microsoft Outlook for Mac
Instructions for Outlook 2011 on OS X
- From the menu bar, click Outlook and go to Preferences.
- Click the Accounts button.
- Click the + button, and select E-mail...
- Enter the details for your account as follows:
- Email/Username: Your Google Apps email address
- Password: Your Google Apps password
- Type: IMAP
- IMAP Server: imap.gmail.com
- SSL Enabled, Port 993
- SMTP Server: smtp.gmail.com
- SSL Enabled, Port 587
- Ensure the Override default port and Use SSL to connect boxes are checked.
- Click Add Account.
- Select your newly added account from the list. In the right pane, select More Options... under the SMTP settings.
- Set the authentication option to Use Incoming Server Info. Click OK.
- Close the preference pane to begin using your email.
Option 2 : Using Google Mail with Mac Mail
Instructions for OS X 10.5 - 10.7
- Go to System Preferences
- Open Mail, Contacts & Calendars
- Click the + to add a new account
- Select Gmail as the account type
- Enter your details, click Set Up
- Select the items you would like to sync
- Open Mac Mail to begin using your email
Instructions for OS X 10.8
- Go to System Preferences
- Open Mail, Contacts & Calendars
- Select Gmail from the accounts list
- Enter your Google Apps login details
- Select the items you wish to synchronise
- To sync contacts, open the Contacts app.
- Go to the Contacts > Preferences menu.
- Switch to the Accounts tab
- Click + to add a new account, and select CardDAV as the account type