I mentioned before about the difficulty of running private email
servers [0], including the fact that I no longer recommend it to
others. I should have taken my own advice, because a recent email I
sent to a friend with a hotmail account bounced:

    550 5.7.1 Unfortunately, messages from [x.x.x.x] weren't
    sent. Please contact your Internet service provider since part
    of their network is on our block list (S3150).

Which includes a block to all of outlook, hotmail, live.com, and any
other MS email domains. So I submitted the bullshit form to take
care of things... but after a few days they replied and denied my
request!

So now I have a support ticket open with 'Outlook.com Deliverability
Support'. This is all so pointless, my own domains are setup with
all of the right mail server-y things one should have nowadays -
spf, dkim, reverse DNS, TLS sending, etc., and I've had the same
mail server IP for _years_, so it has not, in recent memory, ever
been used to spam.

I think the main problem is that the IP reputation DBs don't track
smaller servers, so when the big providers go to check an IP, they
get no data. Rather than assume no reputation data is good, they
assume no data is bad, and blacklist you.

[0]: gopher://gopher.unixlore.net/0/glog/private-email-servers-dying.md