That's a number which is trivially calculable. I don't know what it will be yet, but if you asked me to pick the over/under, I'm in for 80 out of 16k people on our list at present. An unsubscribe is not "I hate you guys and wish you would die in a fire"; it's the email equivalent of a browser's back button. "Not for me, not right now." Many startups let each unsubscribe punch them in the gut. Don't do that. The only way to avoid unsubscribes is to avoid email. You profoundly don't want to avoid email.
We've sent ~2 emails since... March? If I were a consulting client of myself, I'd have written somewhere between one and two dozen.
Is this email going to produce business results for the company? Hard to say. Wild guess? I get a contact in the next hour from one of the companies who has a stalled LOI saying "Oh great you're shipping let's get that signed." Depending on which company that is, the economics are worth hundreds of thousands of dollars.
Many professional email marketers strongly disagree with writing long emails. I will chalk that up to a respectable professional disagreement. They work very well for me, by any trackable metric and by most of the intangibles. I've never felt like I created much value with the little 125-word-and-a-picture squibs that the industry blasts out by the hundred million; I know (because people tell me) that some people like my writing rather a lot and are disappointed that I don't hit them with 8k words every Friday. As it happens, a portion of Starfighter's list is folks who are in exactly that bucket.
Does that answer the question? Not trying to be very defensive about this, just trying to help other startups out. The modal startup sucks at email marketing. It is, far and away, the highest ROI channel you have and probably the easiest to use well. You should send more email. You should send better email.