so my instinct for a while has been that Substack have been damaging their sender reputation by offering unlimited free sending to unlimited recipients, with the upshot that they attract a lot of people sending low-open-rate, marked-as-spam or marked-as-promotional emails. (They also, to my knowledge, won't let senders use their own email addresses, all emails are sent from Substack).

I realise it's much more complicated than this, that within a given ESP there are multiple bundles of senders and that better customers get moved to a better bundle etc, but my guess is that for any given level within Substack you're being bundled with an unusually-bad group of peers and therefore getting lower open rates -- I would love to know if this is an accurate understanding, or if there's any accurate way to test this from outside Substack.

> sending low-open-rate

This is a great theory. I'm subscribed to a bunch of Substacks, and most send fewer but longer posts which I always open and read. While others treat their Substack like a Twitter feed and send out lots of short posts a day which I hardly ever open.

Alex Berenson has already sent me 3 mails today, and the day isn't over yet...but there are other lesser known people who send far more. And some of those others are crypto/forex/finance writers who by the nature of their content, spam filters may view more suspiciously.

Good theory. Even my Substack subscriptions land in Promotions on GMail.

Buttondown is less known, so it's trackers are less likely to be blocked