How to schedule an outgoing email through Gmail:
https://support.google.com/mail/answer/9214606?hl=en&co=GENI...
through Outlook
https://support.microsoft.com/en-us/office/delay-or-schedule...
through Apple Mail
https://www.igeeksblog.com/how-to-schedule-email-on-iphone-i...
through Proton Mail
https://proton.me/support/schedule-email-send