Admittedly the title is pretty sensationalist. The repo activity seems to indicate that the project has some users. It's impossible to know how many sites or which sites block emails contained in this list and what the impact might be. Even though I think the 7c/fakefilter project is inane, I would hesitate to say there would be no consequences at all.
It's best to defend legitimate email providers whenever possible. If we don't, those with an axe to grind get to define the provider's reputation.
There's quite a bit of misunderstanding in the comments.
The kernel maintainers usually do not work for the Linux Foundation. Linus is not their boss. In this case, you notice that Mauro has RedHat.com email address. Most kernel developers submit changes to the kernel as part of their duties with their actual employer.
Linus managed the project and repositories that kernel developers were submitting changes to. That's it. Linus has no power to fire any of them. The worst he could do is refuse to merge any future code changes from the dev that did/said something stupid.
If Linus hurts your feelings you have two options: do better or stop contributing.
The message is more of a forum flame than an inappropriate message between a supervisor and a subordinate. This message is not a direct email leaked to the Internet. This was posed to Usenet, an early type of public discussion forum which is now more commonly used for piracy than exchanging messages. Here's the entire thread: https://lkml.org/lkml/2012/12/21/430
How many times have you lost your shit on someone on a forum because they did/said something stupid?