[motdiem]

Booking.com also has some really bad checking for email adresses, which is why I often find reservations in my account for people who enter my email adress instead of theirs in the booking email field (I have a booking.com account with that email, they don't, but the booking still gets tacked to my account - it cost me nothing, but I could change their reservation if I wanted to)

[scurvy]

Same with Vanguard and Fidelity. I could steal someone's funds if I really wanted to.

Now that I think about it, Quicken and TurboTax too. People signed up for all kinds of important things using my email.

[crtasm]

Same with airbnb, you can book and have the host confirm booking without any checks your email address is correct.