One of the nice things about Gmail at the time, was that you could access your emails when not home. If you were at a friend’s or on holiday at a net café, all you needed was to know your email and password.
That sounds silly, but at the time the majority of ISP mailboxes were pop only. Or those Webmails you could get were attached to what you would now think of comically small mailboxes. Full history Webmail added a convenience we didn’t get before.
That requires more circuitry. Just have the computer check every 0.25s, and if you have depressed the button it is a 1, else a 0.