Astro is currently the best email client out there for Gmail (and I believe 365) accounts. They are still in Beta and are near full featured. It allows to send later, snooze and set reminders.
In addition to being a great standard client, it has built in AI that is only getting better as the days progress. It helps you quickly find action items in your email, set appointments and decide what is important. If you have macOS or iOS try it out.
