> Is the fear of "people selling your email to spammers" a modern myth, or are spam filters that good?

A decade ago I worked for a service that let you send bulk emails.

Any time we thought a customer was using a purchased email list, we came down on them hard or booted them off the platform. Same for other forms of spamming, not including an unsubscribe link, etc.

This wasn't necessarily altruistic: if their emails were marked as spam it would poison the reputation of our sending IPs and threaten the business.

It's clearly imperfect, but the industry's incentives seem to help.