It's scarey stupid how much the "big 3" own email now. Google, Yahoo, Hotmail. When any of them change up their spam fighting techniques it causes ripple effects across the entire email ecosystem now.

Have Yahoo mail subscribers on a Mailman mailing list? Not if you're not running the latest Mailman which has a new workaround just for them. Yahoo started bouncing legitimate mail a couple years ago due to the normal way mailing lists have ALWAYS handled sender addresses, since before Yahoo existed.

I get it, sometimes desparate times call for desparate measures (for fighting spam). But jeeze, it's super annoying to have to break your package manager to get an upstream mail server to support one user who uses one certain mail hosting service.

I send newsletters (that people double opt in to and want to receive) to about 360k developers each week and a good 90% are on Gmail or have their domain on Gmail. This is very specifically developers, however.

In the younger, private mail account demographic, I’ve seen as much as 80% of some e-mail lists being Gmail accounts. For business, Exchange is still king, but Gmail is gaining on them.