> There's no "Send after X duration" or "Send at X time", so you can't write something at 3am and schedule it to be sent during work hours.

You can though. Gmail supports the open source protocol called IMAP(v4) and SMTP. You can use a different MUA than the webmail one, such as (partly FOSS) Mailspring, which has this feature. Heck, you could even use 'at' to send an e-mail from CLI, using any SMTP server you got authorized access to (including Gmail).

> I've said the same thing about FastMail before, these email guys SUCK at innovation.

I don't know about that. I've never used FastMail. I do know these FastMail people are behind JMAP [1], a successor of IMAP4. They're behind the IETF draft of it as well.

[1] https://en.wikipedia.org/wiki/JSON_Meta_Application_Protocol

Agreed on the point about maintainance!

As to your other points:

* There actually is a "scheduled send" send feature, but it is a bit hidden: The "Send" button has a little dropdown arrow, there you can select "scheduled send". Don't know how long that has been there, I remember missing that feature, too.

* There is "confidential mode", which I haven't used extensively, but that might be what you are looking for. It's one of the buttons next to "Send".

"* There's no way to add private notes to email threads. So if I'm told something over the phone which is relevant to the email conversation (but private), I have to dump it into some other notes app where I'll lose it."

There are several extensions available which add this ability. Two are "Simple Gmail Notes" and "Gmail Notes". There are several others. Some free and some paid.

Alternatively, I will reply to myself at that point in the thread. Just have to make sure you don't include this when conversing later, which isn't a problem as I generally reply to the other person's inbound.

Sending myself emails as notes is the stickiest note taking app I've had in 20+ years of internetting.

> There's no "Send after X duration" or "Send at X time", so you can't write something at 3am and schedule it to be sent during work hours.

Actually, this exact feature exists:

https://support.google.com/mail/answer/9214606

> There's no "Send after X duration" or "Send at X time"

They added scheduled send recently. https://support.google.com/mail/answer/9214606

> * There's no "Send after X duration" or "Send at X time", so you can't write something at 3am and schedule it to be sent during work hours.

I have this feature. Next to my Send button is a dropdown to Schedule Send at a time.