Yes that’s correct. Email senders are informed when you mark email as spam so they can add you to an unsubscribe list automatically.

This is very odd. I thought the "mark as spam" button was entirely within Gmail. I had no idea it sent a message to the email sender. Is this standard? It seems counter productive, since it confirms the spam was received. I want it to fail silently and disappear forever.

What should I be doing, to achieve silent spam disposal within Gmail?

I hope I don't have to set filters myself, that would defeat the entire purpose of a smart system that learns to recognise spam.

Edit: we're talking about "mark as spam", not "unsubscribe", right?

Yep.

Sounds like an easy way to verify active email addresses.

It is! But it's better just to check the SES queue for "email was delivered".

Yeah the SMTP protocol handles verification of mailbox existence already.

Gmail parses the email for an unsubscribe link and asks if you want to unsubscribe. If you say yes, it follows the link for you.

See this: https://lifehacker.com/5319723/gmail-offers-to-automatically...

Yes, although I'm asking about marking spam, not unsubscribing.

That's when Gmail prompts you...when you initially mark it as spam.

The next time you get such an e-mail, look through the headers (available via "Show Original" in Gmail, IIRC) for a "List-Unsubscribe:" header.

This value will usually be an HTTP URL (it can also be a "mailto:"). That (unique) URL (which is tied to your e-mail address) is then followed in order to unsubscribe you from the list.