Samsung Flow - Android and Windows Apps.
SendLater - Email scheduler for Mac Mail.
Right Inbox - Schedule Emails in Gmail To Be Sent Later
Huawei Mobile Services - Huawei Mobile Services app comes up with features to help you in accessing a large number of advanced features such as payments, push notifications, and Huawei ID, etc.
SndLatr - SndLatr is a Gmail plugin that makes it easy to schedule emails to be sent automatically at a later time.
Samsung Email - Samsung Email app enables users to receive, manage, and send all the important emails from as many email accounts as they want.