I used to get an email when I submitted a new diff and when reviewers commented but that is no longer the case.
It started sometime during my work on D2525. I don't remember if I received an email for @erikd's comment (Sept 11, 2016) but what I know for sure is that no email was sent for @simonmar's change request (Sep 12, 2016).
This should now be fixed. Apologies for the wait -- you got trapped by the Mailgun suppression filter, because apparently some emails bounced off your user account @acm.org -- I imagine the SMTP gateway might have been down at some point and you probably don't need many CC's in that time window to get blacklisted.
I'll be contacting Rackspace and looking into what we can do about this on Mailgun's end (it's apparently not possible to easily share a team account with Rackspace/Mailgun SSO, making things complicated for anyone but me to un-blacklist you. The API key support is also somewhat limited, it seems). If necessary we can always script against the suppressions API (and this might be easier in the long run, because their UX for search terms is fairly finnicky -- easier to just download a shitload of JSON and post-process it manually).