Upvoted you too! :)
Spamassassin is half of the bane of my life when it comes to maintaining deliverability on a scientific mailing list:
It stops being a useful tool and starts being a mode of censorship that is in effect controlled by the people who practice fraud and abuse. It is very annoying to find all sorts of things that effectively can't be discussed by mail in a list: specific drugs and technical terms used in research, any research discussion or published research that uses long technical words in close proximity, fundraising for research, and so on and so forth. Every newsletter to the opt-in, well-gardened list becomes a little minefield of self-censorship as you go through multiple iterations with spamassassin, weeding out and rewording things.
It is all very trying. One has to think that there's a better way.
But, even scoring 9/10, I still have a lot of trouble sending mail to people on hotmail/live/outlook. I have contacted Microsoft and after getting the advice to not send bulk mails (I don't) a couple of times, I finally got a human to respond. This person admitted that their spam filter is an outsourced black box over which they have no influence. I should try to use proper formatting and hope for the best...
So I don't know how useful this score is in the real world.
Edit (some more mail server pain): The first mail I sent from my own server was a mail to all my friends informing them of my new email address. at that time I didn't have spf configured and used a self signed cert. So I would be 7/10. All Yahoo contacts answered me that I was permanently banned. None of them ever receive any of my mails.
Microsoft seems to have lots of secret rules, blocked IPs and other stuff that nobody's really figured out.
I did manage to contact them one, I got white-listed, and email went through. But only for a few months, and then it went back to being silently dropped again. It was only for a particular domain. Other domains on the same host has no issues.
I had to move the client in question to Fastmail, since there seemed to be no way to figure out how to please MS, and my client had lost several big sales due to documentation being silently dropped. Fastmail deals with it somehow. I guess they have some human contact with some influence in MS anyway, being large as they are.
As an alternative to this, if you'd like a little finer grained information about it spam filters from specific companies, Litmus (I'm not affiliated) has a really cool spam-test that actually tests it against all major spam filters (Google, Yahoo, etc) instead of testing it against spam lists like this does.
They can easily ignore DMARC records, but at least you're still telling them what to do with failing email.
Much like a scalpel can be used to save lives of kill people.
My SaaS has a built in marketing tool that allows for bulk email sending. I constantly run into an issue where customers have an image from a designer, and want to embed that image as the entire content of the email. Of course, that's flagged as spam. I would love to show users a spam score before they blast away.
Case in point is REI. A couple weeks ago I spent several hundred bucks on camping gear from one of their competitors and found out later they'd had an enticing discount linked in one of their image-only emails. I guess we both lost out.
It really makes a huge difference getting past spam filters everywhere, so I can't recommend this website enough!
Can't recommend these kind of tools enough!
Gmail might be making this a little better by introducing a middle ground, moving those kinds of emails out of the Inbox into either the "Social" or "Promotions" boxes, where they're less likely to be marked as spam (although probably also less likely to be seen).