I'm using Mozilla Thunderbird, which provides exactly that option on a
message filter. I've been using it for a while, and it seems to be less
than perfect in ignoring messages. However, there's also an annoying
consequence. I normally set "View/Threads/Threads with unread". However,
messages on the subthreads that I've ignored apparently count as
"unread". I've tried "Mark as unread", but that only affects the
messages I've filtered out directly - replies on the ignored subthreads
still cause the thread itself to be treated as containing unread
messages, even though I can't see those messages.