Boomerang

Boomerang is one of the older inbox add-ons for Gmail and Outlook. Its core idea is simple: when you send something important, you can tell Boomerang to bring it back to the top of your inbox if nobody replies by a date you choose. You can also schedule emails to send later and snooze incoming mail until you need it.

Respondable, part of Boomerang, reads your draft as you write and suggests changes that it says make a reply more likely, such as length, subject line and number of questions. Treat those suggestions as advice.

There is a free tier with a limited number of uses each month and paid plans for more. It works in the browser for Gmail and as an add-in for Outlook; check the official site for supported versions.