Can't "unblock" an email address

I receive loads of unhelpful email from the NextDoor web site do I blocked them.
I now need to login to the site, but they send an email with a verification password.
All such emails are blocked.

I’ve scanned high and low and can’t find a way to unblock this email.
PS:I was once a network engineer so I’m quite comfortable navigating configuration screens to find some obscure setting. This one has me stumped.