Maybe someday you want to postpone sending email, even if the email has been written but you do not want if the email sent at that time, but you have to leave the room or office. For this purpose you can do it by setting the email sending schedule, so the email can be sent directly (hit send button) on the spot, but the new system will send it according to the time we set.
If you use Gmail, there is currently no menu in Gmail for the delivery schedule or to delay email delivery as desired above. If using third party services there are many who provide but not all of them are free and you have to think about the security / confidentiality as well.
For the trick you can use Microsoft Outlook because in Outlook there is Delay Deliverymenu to delay sending email.
Live Gmail settings in Ms Outlook, then set its delivery delay .
For how Gmail settings in Outlook can be seen in previous post Gmail Settings in Outlook with IMAP
And for how to postpone email delivery can be seen on Setting Outlook email delivery delay
