Multiple email notifications for cert expiry

[humphd]

I woke up to 3 duplicate certification expiry email notifications from prod today:

It looks like we still need to do more work on this. It looks like they all came at the same time.

[SerpentBytes]

I am assuming we are still creating unique jobs, which is why we are still getting dupe emails. I could start to look into this later today.

[humphd]

It could also be due to running multiple instances in prod (i.e., we have 2 instances of our server running, both using the same Redis backend). But having 3 of them is interesting, since that means it's potentially more than 1 thing.