Downvotes should be reserved for things like Spam, Plagiarism & Phishing.

I disagree with this one:

LN isn't the same as Hive, people take the same share from the same pool when it comes to mails/posts. So, when I read your stories and posts and then see someone's "post" being just 30 new words and the rest is filled by either copy-pasted messages or links to posts they haven't read. They're getting downvoted. There are reasons to downvote mails outside what you just mentioned. Although I could make a case to include those kinds of posts under spam, to be honest.

Regarding letting the downvoted know, here's the issue. The last time I did that, I ended up with 30+ downvotes per mail. I had my rep go from 100 to 0 in the span of 2 hours.

Speaking as a guy who gets 9+ DV average per mail (Not counting Solo)

People have their reasons/criteria to downvote. Maybe if there wasn't such a retaliation culture, we'd have that open dialogue you wish for. But, either way, although people love pretending the downvotes they receive are senseless, I think in most cases it is easy to figure out why it was done whether it is sharing someone else's post, lazy posts, or old posts (the reason I get downvoted), and so on.

Either way, your mail has proven quality, and you should be safe for the most part.