Delay receiving emails on Mail since installing Big Sur

Try the following:

1 - log into another vanilla admin user account, Set up users, guests, and groups on Mac,  and see if the problem persists. (This tells us if the problem is limited to your user account or is system wide).

2 - boot into Safe Mode by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

And no, I'm not a bot and neither is Karina184. Lose the attitude, we're trying to help.

Hello MarkSefton,

Thanks for using the Apple Support Communities. We understand that you're having issues with email on your Mac and iPad. What type of email account is this happening with? Is it iCloud, Gmail, or something else? Do you have multiple accounts within the Mail app? If so, is this happening to all of them or only a certain one?

For you Mac, have you tried using the Connection Doctor to see if any issues are indicated? You can read more about this in article, If you can’t receive emails in Mail on Mac.

You can use the actions provided in, If you can't receive email on your iPhone, iPad or iPod touch to help with issues related to that device.

Regarding all devices, have you checked to make sure your Mail settings are correct? You can use the Mail Settings Lookup to confirm.

Best regards.