Anecdotal, but I have had better luck sending through an email provider to Hotmail (and Outlook.com and friends) rather than setting up my own outbound SMTP. I've used both Mailgun and Mandrill – of course, make sure you set up SPF and DKIM with the provider, too.
Yes I already do this - still doesn’t solve the hotmail junk filter hell.
The emails I send are not newsletter, just invoices and the like. They go through fine to gmail, yahoo, etc, but for no known reason Microsoft’s useless filters marks them as spam. Of course the average hotmail user never thinks to look in their junk mail folder no matter how many times they are told :(
Interesting, I had no issues with GMail and Hotmail/Live/Outlook.com but with Yahoo. A handful of Yahoo user that mark their own registration email as junk is enough that Yahoo add the domain to their junk filter. It doesn't help that Yahoo has a very prominent "Spam" button in their UI (in GMail & Outlook it's on a drop-down menu).
I have issues on occasion with yahoo, but it is only for a week or so at a time. Microsoft consistently gives me issues. Of course all my test emails to my hotmail test accounts go through without any issue. From what I have been able to determine the filter only appears to be trigged on a certain percentage of email accounts.
