I specifically dislike it when they sent emails persistently with content along the line of "Maybe you have not seen my previous email?"

The second reason that I do a report-spam is when google cannot automatically unsubscribe and a browser tab opens and I should type an email address and confirm.

The worst are the ones that send back a confirmation that I have unsubscribed.

There are some pretty big names in oss with enterprise offerings that are doing this kind of communication.