

600k people being jailed? Very unlikely, the UK doesn’t even have 200k serving police officers in total and prisoners have been released early because there’s simply no space left for them. I’d be surprised if even 1% were arrested. The UK brought in some super draconian protest laws recently though, so no doubt there will be some, especially given what the protest is for.
There are definitely gatekeepers. Even if your hosting provider isn’t blocking port 25 by default, SPF, DKIM and DMARC will see your emails going straight into the recipient’s junk folder/spam filter if not correctly configured. Hosting your own mail server at home is also a fantastic way to piss off your ISP, lose emails to downtime, have your IP blacklisted from many services and open up your environment to exploitation. It can be done but let’s not pretend that it’s easy or that there aren’t barriers to entry.
Mail servers are like filo pastry. Sure, you could go to the inconvenience and effort of making it yourself and I’m sure it’ll be very satisfying to do so. But 99% of professionals use the store bought version, and for good reason, because it’s a lot of effort for an end result that is no better and in all likelihood probably worse.