Apologies for the delays you're seeing.  I have seen others here in the community reporting similar issues during the last few weeks.  My honest suggestion would mirror what @PaulNagami said.  For things that are urgent, I'd recommend using the Canvas inbox directly rather than replying via email.  The email responses do seem to all come in eventually, but it could take a few hours.  I think it's likely server load related, and hopefully something that will get better over time, but I suppose we need to live in the now.

-Chris