Devise a systematic way to check the status of notification emails

[reginafcompton]

Follow-up to issue #126

How can we quickly know if users are not receiving notification emails?

Some solutions:
(1) Every day, put an email into the Redis queue, and check for that Redis completed this process.
(2) Every day, send a test email (making use of Redis) to a real email account. (The problem here: this will quickly grow redundant and the human required to check the email may start to casually overlook it - whether present or not.)