Got curious, tried to figure out what exactly is being blocked, and came across this, unsure if it just applies to emails, maybe not: https://utcc.utoronto.ca/~cks/space/blog/sysadmin/OnBlocking... (https://hastebin.com/share/fipayoqofo.vbnet)

> [...] An open Internet is a great thing, and it would be nice to have one. But it is now less and less compatible with running systems that are useful to their users. I hate firewalling off large chunks of the net from our mailer, but I would hurt even more from our users fleeing email because of spam. And so I firewall. [...]