Send security-centric email notifications

[aaomidi]

For example, in a scenario like this:

Account A issues a cert for a DNS name Z Account B issues a cert for DNS name Z

Notify Account A (after passing some heuristics) that some other account has issued a certificate for a DNS name that they have issued a cert for.

[jsha]

One specific heuristic we want: Only notify if account A issued for Z twice or more (since there are a handful of setups that throw away the account key after issuance).

Also did you mean Z in the second case instead of X?

[aaomidi]

Also did you mean Z in the second case instead of X?

Yes. Updating :D