Avoid live.com at any cost if you care about your emails

A friend of mine has a live.com email address. Turns out, we're blocked by them:

xxx@live.de: Connected to 104.47.5.33 but sender was rejected. Remote host said: 550 5.7.1 Unfortunately, messages from [78.46.34.175] weren't sent. Please contact your Internet service provider since part of their network is on our block list (AS3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors . [HE1EUR02FT029.eop-EUR02.prod.protection.outlook.com]

That surprised me a bit, but what do I know? So, I went to see who else did blacklist us: Blacklist Monitor Report - 78.46.34.175

No one else. Oooookaaaaaayyyy?

So, I tried the URL given in their SMTP response . I don't see any reason for blocking us, as none of their error codes is stated here. We also use SPF:

$ host -t TXT mulle-kybernetik.com
mulle-kybernetik.com descriptive text "v=spf1 ip4:78.46.34.175 a mx -all"

After a bit of searching I came across Office 365 Anti-Spam IP Delist Portal

Fun fact: This site sends a confirmation email which is dropped by our (very standard) SpamAssassin with a score of ~11.x (5.0 being required for being identified as spam). 🤦

Some more digging around led me to the Microsoft community forums, i.e. Delist IP from Hotmail Block List … my overall impression of the discussion is this: Microsoft's blacklisting process is utterly intransparent and they don't have any working process in place to help you getting delisted - if that's possible at all, which seems to be highly questionable.