all your film cameras don't stop working when digital came out.
An analogy to HTTP might be if browsers stop accepting HTTP and only acknowledge HTTPS to exist (mandatory web-wide encryption on anything except localhost/designated intranet IP blocks). At that point you are forced into one walled garden or another - there may be good actors like Lets Encrypt but you are still forced into either their garden or someone else's. The days of running the web server in your basement with no say-so from anyone else would come to an end. And I think maybe in the next 10 or 20 years we start moving towards that.
The film cameras didn't stop working when digital came out, but nobody will develop your Kodachrome anymore. You can also run your SMTP server and send packets into the void as much as you want.
I do it all the time (from a VPS), it requires crossing all the Ts (SPF, DKM, etc), but never had any issues with Gmail, only with other self-hosted systems.
> The days of running the web server in your basement with no say-so from anyone else would come to an end.
That was never true, you had to have permission from your ISP, and many forbade it (and some outright blocked those ports).
Gmail from a VPS has been a problem for me though, Microsoft mail has been worse (yes I look after the jots and tittles).
"Sky Broadband is for private use by you and members of your household only. It must not be used for any activities not reasonably expected of someone using Sky Broadband for domestic purposes."
They're not as explicit now, but all contract and AUPs include terminology like "damage our networks", which cover poorly set-up and poorly run servers.
I don't know about that -- I've been running a webserver (as well as a few other servers such as email) using my residential ISP for decades, spanning several different ISPs including major national ones. It's never been a problem.
It doesn't?? Weird, because email is still the communications service that I use the most.