Microsoft (Live/Hotmail/Outlook/...) is the single worst offender against small mail servers. I have run a mail server for the last ten years spam-free and vuln

Microsoft (Live/Hotmail/Outlook/...) is the single worst offender against small mail servers. I have run a mail server for the last ten years spam-free and vulnerability-free. It has never been on any spam blacklists, delivery to GMail is just fine. I have implemented everything from SPF to DKIM to correct rDNS. Yet, my IP address predictably ends up on Microsoft's "blacklist" every two months or so because of "spam behaviour or user complaints". I am rather sure that neither is true. Every time I have to fill in their appeal form, get unlocked immediately but have to do the same dance again two months later. They have every right to reject a mail server but at least they shouldn't lie about the reason. My server's IP address gets blacklisted again and again even during months I don't send any mail to Microsoft addresses.