Many services require email confirmation, that is right. But this is not required immediately. I can do this hours later. Some services even allow it to do days later.

Yeah fair enough. I’ve never used Greylisting before, is there not some folder you can go to to view the emails which have been deleted due to first contact? Like the spam folder or something?

That isn't how grey listing generally works, no

Even in the case of a long delay - this is a one-off event, as opposed to login which could be a daily occurrence.

My understanding of Greylisting is that there’s only a delay the first time someone contacts you so this shouldn’t be a problem

That's not the only reason emails may be delayed.