IMO, if the HA system is behind a firewall/NAT and you trust that barrier, you shouldn't need to touch Linux unless something needs updating for other reasons. I assume anything behind my router is secure/not malicious so I don't add real security to my HA system. If something breaks, I will swap in the backup SD card and restart. If there's an attack from inside, I've got other problems.
So, IMO the issue here is getting a stable installation that includes email notification support that functions. I have a working instruction set for Wheezy circa 2015 but when Linux updates are installed, it breaks them. The instructions are for people installing a new instance of HG today, so it would be ideal that those instructions could be used...today. I can update the instructions to remove the mozroots line (which I believe you are saying is the issue). But, my point with Jessie is that although HG hasn't been tested thoroughly on it by Gene (that we know of), it's really the option forward for the RPi.
I posted the instructions to provide a useful guide for others and myself. If they don't work, that's frustrating. I just want to make sure my instructions still work and, if not, fix them in as minimal a way as possible for now.