[gakos]

You can set reminders for emails to come back to your inbox both at send and separately when reviewing email. It also has read receipts. And the hotkeys and shortcuts are super powerful. Worth the $ if you have to spend a lot of time in email for the efficiency increase alone.

[Fire-Dragon-DoL]

It's not the reminder of emails that the OP is talking about. You can do that in Gmail. It's the freedom of adding any reminder to your inbox, not related to emails, that made a huge difference.