Send Later is a very simple plugin for macOS Apple Mail with 2 main features
It allow to prepare your email and send it later at a defined time and date.
Great for working with people in different time zones and managing the time you spend on emails.
It allow you to set a delay before sending an email (ex. 60 seconds) so in case you forgot something, you can still prevent the email to be sent.
Useful to prevent missing email attachment.