[i_am_jl]

They can, but they have to ask a court to enforce any sort of block. I imagine that's coming soon.

[lawlessone]

Now that you mention it, that's probably why they sent this letter. They know it's pointless but they want a paper trail to show they tried to find other solutions before requesting a block.

[rbanffy]

It's entirely up to 4chan to voluntarily comply and avoid any further consequences.