I have already spent too much time trying to get Microsoft to
unblock my email servers, which do not seem to have a reputation for spam anywhere and don't even have enough of a sending record to be
rated yet by Brightmail. ...but Microsoft sends me this, 24 hours after I request an unblock:
Dear Woozalia Staddon
We have completed reviewing the IP(s) you submitted. The following table contains the results of our investigation.
Not qualified for mitigation
165.227.176.23; 45.55.148.146
Our investigation has determined that the above IP(s) do not qualify for mitigation.
Please ensure your emails comply with the Outlook.com policies, practices and guidelines found here: #^http://mail.live.com/mail/policies.aspx.
To have Deliverability Support investigate further, please reply to this email with a detailed description of the problem you are having, including specific error messages, and an agent will contact you.
Regardless of the deliverability status, Outlook.com recommends that all senders join two free programs that provide visibility into the Outlook.com traffic on your sending IP(s), the sending IP reputation with Outlook.com and the Outlook.com user complaint rates.
Junk Email Reporting program (JMRP) When an Outlook.com user marks an email as "junk", senders enrolled in this program get a copy of the mail forwarded to the email address of their choice. It allows senders to see which mails are being marked as junk and to identify mail traffic you did not intend to send. To join, please visit #^http://support.msn.com/eform.aspx?productKey=edfsjmrpp&page=support_home_options_form_byemail&ct=eformts.
Smart Network Data Services program (SNDS). This program allows you to monitor the 'health' and reputation of your registered IPs by providing data about traffic such as mail volume and complaint rates seen originating from your IPs. To register, please visit #^http://postmaster.live.com/snds/.
There is no silver bullet to maintaining or improving good IP reputation, but these programs help you proactively manage your email eco-system to help better ensure deliverability to Outlook.com users.
Thank you,
Outlook.com Deliverability Support
I
already included the error message in my original problem report,
where it says "copy and paste any error messages":

This looks to me basically just like the big players trying to keep out the competition. They're blocking unknown servers
by default, making it basically impossible for anyone without an IT department (aka the resources to deal with this level of hoop-jumping and or possibly twist some arms or grease some palms) to offer reliable delivery to Microsoft addresses.
Google is nowhere near this bad, but they sometimes reject messages from my servers too. So does ProtonMail, and some Yahoo relays do as well.
I'm not sure what an appropriate response is here, other than the obvious one of destroying all capitalism and requiring companies over a certain size to be controlled by the people they supposedly serve;
working on that.