I use a tiny ISP and have only once or twice had the "Hotmail doesn't like your address" thing.
Given that Spamcop catches around 300 spams a day to my various addresses, many of those with "Hotmail" as the (possibly forged) origin, it does seem that pots are maligning kettles.
I usually phone the person concerned, tell them Hotmail is rejecting their mail, and ask them if they have a "proper" e-mail address. Most do. Problem solved.
Maybe I'm old fashioned (yes, I know) but I prefer to download my mail, excluding the stuff held by Spamcop, and read it on the PC. I glance down the Spamcop list - there's about one false positive a month among the 10,000 or so spams - and then "delete all". But I get to see all the stuff, in case.
I had a Hotmail address but soon gave up using it. Ditto Yahoo - BTYahoo seems to share Hotmail's trigger-happiness.