@Anonymous User: To troubleshoot the issue please open your Email app > Tap the 3 lines in the top left > Tap the cog in the top right of the pop-up box > Select your email account > Sync Account > On > Swipe from the top of the screen to the bottom > Select 'Sync' from the Quick Settings menu. While you are in the Settings menu please check your Sync Schedule and Sync Period, and make sure you have Limit Retrieval Size set to 'No Limit'.
If the problem persists then check that the phone's Software and the Email app is up to date. Then, go to Settings > Apps > Email > Storage > Clear cache / data and restart the phone. If this doesn't help, try removing the account and re-adding it.
Settings > Accounts and Backup* > Accounts > Email > Remove Account
Settings > Accounts and Backup* > Accounts > Add Account > Email > Register the account.
*(Depending on your Android version, this setting may be called 'Cloud and Accounts' or just 'Accounts').