Gmail app messages aren't syncing

Your internet connection might not be working. To check that you’re connected, try visiting a website in your mobile web browser. If you’re using public Wi-Fi, like at a cafe or library, you might need to load a website to accept the Terms & Conditions before you’re actually connected. 

Also, make sure Airplane Mode is turned off.

Depending on your sync settings, the Gmail app checks for new mail every 1 to 30 days.

1. Open the Gmail app .
2. At the top left, tap Menu Settings .
3. Under "General," tap Data Usage Sync settings.
4. Select the number of days you want to sync.

If you use the Gmail app with a non-Gmail address, like @yahoo.com or @hotmail.com, check your email on a computer to check if the sync issues you were experiencing, like not seeing any new mail, are only occurring in the Gmail app.

If you’re not able to view new mail on the computer, check the support information for your email provider.