[wenc]

I agree with this. The welcome or confirmation email is a transactional email -- I don't really read it (I usually mark as read too -- takes 1 sec), but I expect it to be there.

(This is distinct from an onboarding email. I don't need onboarding emails. Some site combine confirmation + onboarding into a single email -- that's ok with me.)

It's a searchable historical record that I once signed up for something under a certain username. Also, it's important for password recovery and such (not a best practice to be sure, but not all sites support 2FA).