We're glad you had the opportunity to try those steps, Vbjen77.
To confirm, did you have the opportunity to sign out and back in to your email address for the Mail app? If not, those steps are listed below.
- "On your computer, sign in to your email provider’s website. Make sure that all of your email is there or make sure that your email is saved somewhere other than on your iOS or iPadOS device.
- On your device, go to Settings > Mail, then tap Accounts.
- Tap the email account that you want to remove.
- Tap Delete Account.
- Add your account again."
If you've already signed out and back in to your email or the issue continues, the next step would be to reach out to Apple if the issue only occurs on your iOS devices. You can find their contact details via the link below.
Contact - Official Apple Support
If the issue occurs if you were to sign in to the email providers website on a computer, the next step would be to reach out to your email provider for additional support.
Have a great day!