Its trivial, but it's so fucking annoying that I've visualized doing violent things as I hit unsubscribe.
The volume is low enough for now that I still add each sender's domain to our Exchange online's mail flow rules to block with a rejection message to the effect of "The recipient has deliberately blocked cold contact messages from senders such as yourself. Please remove the recipient from your mailing lists.". It brings me great satisfaction to know that going forward system f-off messages are being sent to these people with zero extra effort, or even knowledge on my part.
Gartner tells you what you probably already knew them sells your information.
The email addresses are removed a couple of weeks after the conference ends, which gives everyone time to give their actual email addresses to anyone who contacts them that they want to keep talking with.