How can I send schedule Emails?

As per the title saying Can I send schedule Emails? is there any add-on for that? 
Also, How can I create a “reminder”? 

You write your mail and then go to the register above on “message” and there on “send later”. There you can adjust: Do not send mail before: Date and time.

Let’s say I want to send it one week from today. So should I put the 22th of Nov?

It looks like this - see screenshot - here in German.

Thank you. Are you using this feature? 

Yes, I do.

Let’s say I sending you an e-mail now and At that time I will create schedule mail as well. If you’re replying back to me and schedule will be canceled? 

You can change the schedule. The mail will be in your outbox folder until you want it to be sent by the specified date.

Thanks for the help :) 

Gladly    ;>I