This looks good, but I'm not clear why it's a subscription. I'm happy to pay for upgrades when a new version with new features is offered; and I'm happy to not pay if the new version isn't compelling enough. (Sometimes support for major OS upgrades is enough of a feature.) I'm increasingly disinclined to feed the subscription-based software economy, especially for the personal tools I use.
Yeah -- I was confused too. Is the subscription just for the client, or does it come with an email account?
While Swift Mail is a Fastmail Platform Partner, it is not affiliated with Fastmail (or others) and does not offer email services directly.