The Spark mail client now allows you to send later and have follow-up reminders
Spark
Not for nothing, as the many features it adds update after update give it that merit. In the latest update of the app, we can enjoy two important features: sending an email later and keeping track of emails.

There are certain types of mail that should not be answered at the time or at certain times of the day or days of the week. For example, it is not reasonable to answer your boss on a Friday morning, better to wait until Monday morning. But if you can write the mail on the spot, why wait? Thanks to the latest update of Spark, we can postpone the sending of the mail so that it reaches the recipient at a certain date and time.
Are you waiting for someone to respond to an email? To prevent an important email from being forgotten, the latest update to Spark allows us to add a reminder after sending an email to remind us if the recipient has not responded in X time. This way, we can send a second email to the right person or postpone the reminder to give them more time to respond.
Last but not least, the Readdle team has changed the screen to create a new mail , adding dedicated buttons to reveal the CC and BCC fields. The correction of minor bugs and improvements in operation are also evident.
Remember that Spark is a free application for managing Gmail, Outlook, AOL, and many other email accounts. You can download it for both iPhone and iPad and for Mac, and it doesn’t have any in-app purchase or subscription.
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At Apple