I'm experimenting right now with doing what amount to weekly emails to my newsletter list with new Bookfunnel group promos each time. There are so many in romance it's possible to do that. Since I don't have a cute pet to pimp, and engaging with readers personally gives me hives, I want to see if offering some value will boost my list's engagement. Most of the list is from giveaway promos, anyway. The organic part is <100 names.
What has happened so far is that somewhere under 1% unsubscribe with each email, and about 20% officially open it (although many more may read it). Click-through rates vary but hover around 2%. Sounds terrible, doesn't it? When I gave away a new novella to my entire list--free for all--the click through rate was a bit under 8%, and someone who'd been involved in a similar freebie said that was a good percentage and theirs had done worse.
At the unsubscribe rate above, it would take me a decade to irritate the entire mailing list into unsubscribing, so I plan to keep on sending out the promo info. It's a way of offering something that readers might like. Today it's so hard to find books to one's taste that a promo pre-sort is IMO a valuable thing. I'd appreciate getting the same from the few authors I follow.