Try closing the email app in your multi tasking tray and then turning your phone Off and then back On to soft reboot it.
Then launch the email app again.
Check your email also by logging into it using a tablets or computers Url box and see if your getting emails OK and are able to send them.
If your using the Samsung email app then what I do is go into Settings and then Accounts and delete the email credentials and them re enter them and see if that helps.
You could also try Settings , Apps, email , Storage and Clear Cache.
Current Phone ~Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+ Samsung One Ui 3.1/ Android 11.