I'm feeling a bit thick. Regarding the change to the sign-up process...

Originally:

> Users couldn’t get started on their own. They had to first leave their email address and then wait for me to send them an email with a link allowing them to register and start building their Cortado email.

Afterly:

> As soon as users click the submit button, they get an email verification message in their inbox, which they can click on to set a password and get started.

So, what changed? In both cases users have to submit their email address and interact with a(n) (automated?) registration/sign-up email. In the second case there's the added hurdle of a captcha (which sounds worse).