

I don’t think the SPF / DKIM / DMARC stuff is overly complex nor the core of the problem.
In my case it was recipients with bonkers microsoft exchange servers that just had weird ideas about who should be sending them emails.
For example, one thing that tripped me up forever ago was grey listing. Apparently the receiving server just wouldn’t acknowledge the sending server for an arbitrary period of time, say 12 hours or so. Spam senders would usually give up long before then, while a legit server would keep trying because it’s legitimately trying to deliver an actual email.
So my email-in-a-box type self hosted set up was fine really. Compliant you might say. But to send emails to this one in a thousand recipient I had to investigate what was going on and reconfigure things to ensure their server would interact with mine.
Another thing that can happen is that spammers just put your email address in the “from” field and fire off a few million emails. Obviously the DKIM signatures and SPF won’t match but it still just makes your future legitimate emails look spammy. Having the credibility of a larger organisation goes a long way in this type of instance.
There’s a number of problems with this.
It would only work if enough communities and instances adhered rigidly to similar editorial decisions about what is “political”. I don’t think that’s achievable.
Mods would have to do the heavy lifting in tagging/ untangling things.
It’s not going to be as simple to implement as you think.
Posts are already categorised by community. You can block the vast majority of political posts by blocking a few communities and users.
At times if filtered out keywords like Musk and Trump. You don’t really need to implement a feature for this. Just get posters to include a tag in the title of their post.
Looking at your other comments, you’re not going to be deterred by these criticisms, so my suggestion would be to find the git repo and create an issue to get some proper feedback from other contributors.