its the other way round roberto, the vast majority of servers do allow encryption on port 25, how do I know?

I just look at my email logs, over 95% of mail sent to other smtp providers is encrypted, all of it done on port 25.

For a server to not support starttls now days is not the norm, and typically the result of someone who has not been maintaining their services e.g. plusnet mail.

The "vast majority"??? Maybe of what you use, but the "vast majority" of the hundreds of thousands or even millions that exist that you have used?

How many SMTP providers do you use ? One per mail system is the norm , and if you are meaning customers' systems you have set up then no doubt you tend to use just a few servers.

Server to server I would accept, but that is not what the consumer uses. They just have a mail client to a single server.