Seth Godin has a post up today talking about how friction, that is the cost of sending marketing, is good for marketing. With more friction, marketers make choices about sending instead of sending to everyone.
The post touches on a point I’ve certainly tried to explain to clients and senders in general.

Email, of course, is free.
Except it’s not. The friction that slows down sending email to everyone all the time is the cost of all the people you’ll lose. You might lose them because they unsubscribe, or more likely, you’ll train them to ignore you. Worse still, you might just make them annoyed enough to badmouth you.

Yes! Not only do senders risk alienating subscribers, those non-responsive addresses can turn into a reputation liability. The reputation schemes at most of the major ISPs look at if recipients interacting with email. Training recipients to ignore mail trains the reputation filters that mail, and mail from that sender in general, isn’t wanted.
Senders must implement list hygiene programs and data segmentation to keep reputation high.
Mark Brownlow has more on why list hygiene programs are critical.

hygiene • Reputation • Seth Godin