Awesome! I didn’t realise that it would apply retroactively. I was thinking a normalised address was being saved only for new registrations.
Yeah the main chance of an issue would be for cases of email addresses which allow + aliases but don’t consider periods in different placements to be the same.
All instances of +’s in emails can be handled the same without any issue, as it’s handled the same for all providers that allow it as far as I know. Periods are the only ones where there is some difference between providers.
If I recall correctly, I think Google work emails (using custom domains), Yandex and Outlook will consider different period placements to be different addresses, but the + aliases can still be used.
So the only cases would be like theirs@email.com existing would block the.irs@email.com from registering (when these are actually two unique accounts/addresses according to that email domain/provider). Which should probably be very rare to occur in the real world. 