Each receiving server (SMTP) will incorporate its own set of rules to determine wether a message is spam or not.
ON a clean install of either Windows server or Linux; There is no control what so ever. Any email will be received regardless of content or originator.
So people who start their own mail server on a VPS for example will go and install something like ClamAV mail scanner and spam detector. It scans attachments for infections and possibly some text for dodgy words like pharmaceutics favourites.
But big servers like Google, Hotmail and the likes.. Use their own mechanisms to determine spam content.
Hotmail for example is very suspicious on emails that do not have a SPF record and starts dumping them into spam if many emials like this originate from this sender. They do this because back scatter is a massive problem.. and looking SPF prevents that.
Google- Well they are global and they rely allot on users pressing "this is spam" and they keep a record of email addresses, IP addresses, content and much more to safely determine what is spam and what is not.
The only way - and speaking from experience, is to add SPF, make sure reverse DNS is OK, use a static ip to send emials.. and then contact everybody that you think off and request to get added to their whitelist- and they will verify you.
We send over 300k emails a day(not spam! only to users who want to get our stuff obviously) - sometimes close to a million a week on busy times. And that's the only way could put straight into INBOX.. we still have issues with some ISP's - but that's because they suck.