I unsubscribe from marketing mails, those are legally required to have an unsubscribe link in them. You should try clicking on that if you don't like marketing mail. If they don't stop you can threaten legal action in both EU and US without issue.

If it doesn't have this link, it's spam. If it's trying to get me to buy something I didn't explicitly wishlist on a store, it's spam. If it's unsolicited marketing, it's spam.

And even if I were to include all marketing email, including those I am interested in, then plaintext mail would still constitute the majority of spam mails I receive.

I personally found out that it's easier and faster to train my spam filter to move these mails into the spam folder. (I'm using claws-mail with bogofilter, which works quite well.)

Whenever I have to interact with a company, I check the spam folder for their replies.

The majority of mails in my spam folder is html mail.

It's safer as well. Some (most?) of those "unsubscribe" links have a unique ID hooked in with your email in some database so they know that they have a hit and can send more email to you.

Well, they need something to be able to tell which email to remove from their DB too.

Not all is as sinister as it looks.

The simply solution is to just can any senders that don't respond to unsubscribe requests. But those will be just as bad in plaintext as in HTML, so I don't see why Plaintext means it's not spam, they can do the same thing Plaintext.

The majority of mails in my spam folder is plaintext mail. Second place are the extremely malformed HTML mails. Almost any wellformed HTML mail I receive is solicited at minimum.

I can recommend using the unsubscribe link if you forgot to uncheck the newsletter checkbox during registration. Alternatively send them a mail to A) remind them of the SPAM-CAN act or your local equivalent legislation and B) that they should delete your mail from the newsletter. That works almost always, if not you can always threaten legal action (where I live, that's an easy 600€ of profit in a courtroom).

Any unsolicited marketing is spam, unsubscribe link or not.

That's... what I said. I mentioned the unsubscribe link for solicited marketing mails, where that is in fact relevant. Unsolicited email would be pretty damn illegal in my home country to begin with (and a GDPR violation).

It is illegal but very common. Many of those emails with unsubscribe links are unsolicited. They either spam all their former customers no matter if they have opted in or not or they just buy links. Yes, the unsubscribe links work but what they do is in obvious violation if the gdpr and other laws.

Very few companies would risk those lawsuits, especially in Europe the fines can get rather exponential for repeat violators and I don't think it's much different in the US either. If the unsubscribe works, that is the end of the story for me, and a reminder to check for small newsletter checkboxes when signing up to things.

I very rarely get marketing mails from any reputable company that are completely unsolicited. In most cases it's a followup from trying out an offering or updates to products I'm using or are adjacent to those. If I'm not interested, I either ignore them or unsubscribe if it's repeatedly not interesting.

This is a much more effective "spam" strategy compared to "all HTML is spam".

I have a feeling that they are, in fact, solicited. There’ll be fine print and a checkbox somewhere

Tricked into subscription with dark patterns is not quite the same as soliciting.