If you ever using wifi in the airport or even some hotel with work suite unit around the world, you will notice that Apple Mail can't send or receive emails. It is probably some company wide policy to first block port 25 (that is even the case with some hosting providers) all in the name of fighting SPAM. Pretty soon, 143, 587, 993, 995.... are all blocked. Guess 80 and 443 are the only ones that can go through any firewalls now days. It is a shame really. Hopefully v6 will do better.
So there you go. And know EU wants to do ChatControl!!!! Please stop this none-sense, listen to the people who actually knows tech.
People were (wisely) blocking port 25 twenty years ago.
A network admin can reasonably want to have the users of their network not run mail servers on it (as that gets IPs flagged very quickly if they end up sending or forwarding spam), while still allowing mail submission to their servers.