Is there any way to disable spam filter completely?

Microsoft appears to have changed how the spam filter works. Now if you have email forwarding setup, the forwarding rule will take priority over the spam categorization.

Prior to that "spam" mails would simply land in the spam folder and would not be forwarded. This was one of the biggest annoyances for me.

I can't confirm this behaviour, although it seems that it can take some time (months?  years?) for changes that Microsoft makes to Hotmail/Outlook behaviour to be rolled out across all servers and accounts.  It's a shame there isn't some kind of Help/About version number that we can use to compare any more.

Actually, there is one way, if you use your web browser's "View source" function while in your Outlook inbox and search for the string 'version' (including the single-quotes), you should find a version number beside it.  Mine is 16.1389.11.2087567.  What is yours?

Microsoft appears to have changed how the spam filter works. Now if you have email forwarding setup, the forwarding rule will take priority over the spam categorization.

Prior to that "spam" mails would simply land in the spam folder and would not be forwarded. This was one of the biggest annoyances for me.

I also tested what happens with mails which trigger the virus detection. Those emails will not show up in your inbox nor in your spam folder. If someone wants to repeat the test, this is the site I used:

http://www.aleph-tec.com/eicar/

There are millions of customers who do not want any mail being automatically put in a Junk Mail folder.  MICROSOFT, WHY ARE YOU NOT LISTENING TO THEM?!

Because four years later those customers are still using the service.

And if they fixed one issue, the users would expect them to fix the other issues ! They can't afford the extra work needed to make the web interface of outlook work fluidly, provide a free minesweeper with Windows 10 or make the red cross that should close Skype actually close Skype.

In a classic skit from long ago, Lilly Tomlin explains the MS attitude 

Youtube: phone company sketch - we dont care - Tomlin

There are millions of customers who do not want any mail being automatically put in a Junk Mail folder.  MICROSOFT, WHY ARE YOU NOT LISTENING TO THEM?!

Because four years later those customers are still using the service.

And if they fixed one issue, the users would expect them to fix the other issues ! They can't afford the extra work needed to make the web interface of outlook work fluidly, provide a free minesweeper with Windows 10 or make the red cross that should close Skype actually close Skype.