That makes it a you problem if you delete context, not a problem of the person replying. Deleting context prior to the thread having ended... well. As always, email is very much a personal preference thing. Everyone uses it a bit differently. But your blanket statement that polarian was somehow infringing basic conventions is not really true is it? There was plenty of context for people. If they deleted that or use say gmail that can't do threads, they should fix their setup ;)
