Before you begin these steps please be sure you have already followed the steps in the following articles:
If you have not yet performed these steps, the following directions will not yield the correct functionality.
- On your iOS device, go to m.google.com/sync/settings
- Tap the Sign in with your Google Account button
- Enter your Google apps email address and password and click Sign in
- Select your device and check Enable "Send Mail As" for this device and tap Save
- Mail sent from this device will now use the address you have set as a "Send Mail As" address in the Google Apps Mail settings
Please note: It can take up to 24 hours for this setting to be applied and start working. In the meantime you can test by sending an email to another address you own to confirm that it has started working.