If you can't receive emails in the Mail app on your iPhone, iPad, or iPod touch or Email not working on iphone & ipad there are a few things you can try.

There are a few things to keep in mind and check:

When you back up iOS or iPadOS to iCloud or iTunes, it will back up your email settings, but not your emails. If you delete or change your email account settings, previously downloaded emails may be removed from your device.
Make sure your device is connected to the internet.
Check with your email service provider to find out if there is a service outage.
If you can't access your emails or can't send and receive messages using your email address, find out what to do.

Verify your email address and password
If the Mail app asks you to enter a password for your email account, make sure your password is correct. To check your email address and password, log in to your email provider's website.
If you still experience a username or password error, contact your email provider or system administrator.

Check your notification and get mail settings
By default, the Get New Data setting is based on what your email service provides. If Push is not available as a configuration, your account will default to Fetch. These settings will affect the way your device receives emails. To adjust these settings:

Go to Settings> Email, then tap Accounts.
Tap Get New Data.
Choose a setting, such as Automatically or Manually, or choose a schedule for how often the Mail app will retrieve data.
With iOS 11 and later, and iPad's, Automatically is set by default. Your device will only get new data in the background when it is charging and connected to Wi-Fi.

Make sure the notification settings are correct for the mail application:
Go to Settings, then tap Notifications.
Touch Email then touches an email account.
Adjust your alerts, sounds, and badges.