Hey fredfrommccormick,
We'd be happy to help out. What type of mail account are you using with the Mail app? If this is a preconfigured IMAP account, you might want to remove the account and add it back. Since all the emails are stored on the email server, you can safely do so without any data loss.
If that doesn't help out, or this issue is affecting a POP account, check your fetch settings as outlined here:
Check Mail Fetch and Notification settings
By default, Fetch New Data settings are based on what's provided by your email service. If Push isn't available as a setting, your account will default to Fetch. These settings affect how your device receives email. To adjust these settings:
1. Go to Settings > Mail, then tap Accounts.
2. Tap Fetch New Data.
3. Choose a setting — like Automatically or Manually — or choose a schedule for how often the Mail app fetches data.
With iOS 11 and later, and iPadOS, Automatically is set by default. Your device will fetch new data in the background only when your device is charging and connected to Wi-Fi.
Make sure that your Notification settings are correct for the Mail app:
1. Go to Settings, then tap Notifications.
2. Tap Mail, then tap an email account.
3. Adjust your Alerts, Sounds, and Badges.
All this is outlined further here: If you can't receive email on your iPhone, iPad, or iPod touch
We hope this helps out.
Take care!