As more and more sites upgrade their versions of sendmail, we're going to see more and more of these requests. Rather than asking each of those users to contact their ISP and have the filtering turned off for LJ comment email, perhaps we could change the address that comment mail comes from?
I'd like to propose email@example.com -- that doesn't trigger any of the spam heuristics I can test for, and to the best of my knowledge that shouldn't be all that difficult to set up on LJ's end. It also makes it fairly clear to the user that this is a "don't reply" account.
I can't write a patch for it, because it'd have to be done by someone with server access, but it'd be fairly simple to set up, and it would save tons of time for support.