I think a majority of people don't unsubscribe; they just mark your emails as spam and ignore them. That lowers your credibility with email providers, and if that happens enough, you start seeing your emails being considered as spam and you get entirely blocked off the ISP.

Also, it may be a mistake to attribute all of your revenue from the email to email. By its nature, emails are going to the segment of your audience most interested and most likely to purchase. Only a portion of revenue from it is actually incremental; a large part probably would have ordered anyway, and the email gets credit only because they're also clicking through the email.

Of course, it depends on what offers are in the email, etc. If you want to test, the best bet is as was mentioned elsewhere in this thread, segment out a set of customers and change the frequency of emails over the long term, and track their total sales.

You're talking in general, and most of your points are correct, but they don't apply to our business fully.

For example, our newsletters are always offering a time-limited discount for the purchase. They're also not segmented out to people "most likely to purchase", because we don't have that data. It goes out to 100% of our audience every time, unless they made a very recent purchase.

If we knew who the people are that are most likely to buy, it sure as hell would make the business easier to run.

Yep, you need to track your open rates too. If you have a 20% open rate, run a daily spam trial, and find you had a 0.3% unsub rate but your open rate is now 10%... You actually had a 50% unsub rate, your customers just aren't letting you know they've unsubscribed

Isn’t open rate obfuscated / blocked by most clients now? How do you measure it?

(I’ve been blocking them for 25+ years; might be out of touch…)

Saw this comment late, like tl_donson says, yes but it's fairly consistent. So if your open rate drops 20% to 10% in one month, it's probably your fault and not the mail client hiding it.

In my experience most people do not block images in emails, and that's the easiest way to tell if someone opened your mail. Even most people who use an adblocker do not block email images.

open rates are inaccurate but still somewhat useful because they’re generally consistently inaccurate month to month unless there’s been a change that would affect a lot of subscribers (eg iOS recently).

click rates are probably a better proxy for this.