9.0.2 update caused gmail issues

I encountered the same issue with moving to iOS 9.0.2. I deleted any Gmail accounts on the device and re-added them. This fixed the issue where it couldn't connect to the IMAP server.

Try resetting your Mail Account and system by following these steps (please do not skip any steps). First close your Mail App completely from the multitasking window by double clicking the Home button and swiping up the Mail preview pane up until it disappears from the screen. You may have to look for the Mail pane by scrawling to the left as there may be other panes there from other apps. Then go to Settings > Mail, Contacts, Calendars > locate your email provider and click on the account. Then on the next page Delete Account. Then do a forced restart. Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears. Ignore the "Slide to power off" text if it comes up. You will not lose anything. Then go back to Settings > Mail… and add the account again.