The backflow current from fans is extremely minuscule and extremely unlikely to damage anything from that. There are even tests using a damn leaf blower on the fans and it barely generated any current. Even if it did generate a backflow, diodes on the mobo should prevent it from becoming an issue unless it’s a power so great that it just fries everything, but that’s basically impossible with a fan.

Here’s one such experiment.

https://youtu.be/k9KA-xLLQXo

I don’t use porkbun so I can’t guide you in detail. But look for “glue records”. Some will just call this nameservers, ns record, or some other confusing and ambiguous lingo (like GoDaddy…). Glue records are separate from rest of the auth DNS servers. Even though you are essentially doing an A record.

So if you have example.com on porkbun, and auth nameservers for this same domain is going to be elsewhere, you can set glue records. Like…

ns1.example.com ns2.example.com

With specific IPs like 123.123.123.123

This will allow you to essentially do the first step and not end up in a cyclic problem of one requiring the other.

I assume this is what you’re referring to as the problem.

Never heard of yunohost, but… definitely not worth managing your own email server. That shit is essentially a full time job. And it’s forever ongoing full time job, with 24/365 on call type job if emails are mission critical. Doesn’t matter how much other hosts are charging, it’s worth using third party email service.