EM Mail has worked pretty well for me.

Same. I've been a fastmail user for years and JMAP is a must-have for me now. But infra is so much easier to manage than it used to be, and I see projects like this and I'm thinking it could just be my own affordable box in the cloud now (that I could use for other servers as well).

I've been self-hosting my email for years. Something that wasn't obvious to me in the beginning is that you can separate sending and receiving: host the receiving yourself and use a service for sending (e.g. Mailchimp, Sendgrid etc.). That can address many concerns.

I did that in the beginning but later set up my own relay hosted at Hetzner. I could do it on my receiving server (a PC in my house) but I don't have a static IP and IP reputation is a big deal in email deliverability.

I do very occasionally get sent to spam but it's fairly rare and I'm not sure my free Gmail account was any better.

Even a custom domain can be pain. I have an xyz domain and my mails usually land in the spam folder when I send from it. If you don't have enough volume you might have trouble as well.

Whenever your email doesn't get delivered, you just resend it from your Gmail account. Receiving always works.

Nice. Curious if they will also let Mythos and related LLM's also take a pass at it.