So your ISP is not providing you an internet access ? That's lame.
Also, blocking standard email ports on residential connections is a common anti-spam measure.
Are you allowed to run a game server, ftp server, web server, ssh server ?
Words first mean what is written in a dictionary or encyclopedia.
Internet : https://en.wikipedia.org/wiki/Internet
If you are not allowed to run server, they are WSP (Web Service Provider) not ISP.
But if you are OK with ISP not providing internet, I'm sure you are fine with unlimited limited or throttled after x, 24/24 access between 9-5 and secured http page as long as there is a padlock favicon ...
Nope - this is an important difference between English and other languages. If what people say differs from what's in the dictionary, it's the dictionary that will change, not the people.
Email is a bit less useful when everyone has you auto-blocked for being 'spam'.
An argument that it's not "full" internet access will get you nowhere - very few consumer internet subscriptions are "full" internet access in the sense that they are totally unrestricted - most have very severe restrictions on e.g. running servers and many other things.