Comment by sandermvanvliet

I've had to deal with this with e-mail verification links and Auth0. The user clicked the link after getting it in their mailbox but then Auth0 throws up an error page because the e-mail address has already been verified (by Outlook scanning). The problem becomes worse if for some reason the mail ends up in the junk mail folder so the user thinks they've never received the mail but when you check it looks like the e-mail address was verified successfully. That has caused a lot of annoying back and forth trying to figure out what the hell is going on. We ended up adding a custom page to handle e-mail validation so we could handle the situation where the user lands on the page and the address has already been verified. Super annoying.