chances are: checks it against a database of addresses it has seen before (e.g. because they were used to register stuff elsewhere). No such entry, or entries all younger than n days -> 'freshly registered'.
Sucks for people who don't use their addresses for just about anything.
It is not a healthy idea to prevent access to a trial solely because of a lack of reputation associated with an email. However, in this specific case, if there is a rotation of numbers at the end of the email, tirreno has rules that detect similar email patterns.
Additionally, I assume that registrations are coming from the same IP or network, which should make it simple to detect through platform.