Sometimes people email a reply along these lines:
Joe Bloggs reacted to your message:
It would be cool if Discourse were able to recognise this and treat it as a like rather than a reply.
I don’t know what sort of email client does this (for all I know it they all can now) but I’ve seen it a few times and the emails seem to follow a recognisable pattern.
I also don’t know whether it is possible to send a negative reaction, but I can see that if that were possible it would complicate matters.