You force me to register to see the blurred text.

Ok let's take some time to create a temporary email address because, well, your product looks refreshing.

I put down the email address (the one I just spent time creating!) and a password. Your now reject my temporary email address as being temporary !

If I eventually give up, and give you my real email address, will you send my any email ? That one would be unsollicited, and you can be sure that people who created a temporary email address will mark your emails as spam, which may destroy your sender reputation...

People who give their real email address may not mark your emails as spam. But people who take the time to create a temporary email address will, with very high probability.