Associate Email with open task, and mark it complete.
If I set a task for myself to email my customer on Monday
morning. I'd like the email that I send to update that original task, and market it as complete. Right now I will create a new activity by sending the email, then need to go
close that task separately.
Chris Braun commented
In Gmail, you can currently use the Follow Up Reminders to return the task to your Inbox over creating a Salesforce task. That way you can complete the task and not have to close the Salesforce task. https://www.cirrusinsight.com/support/gmail/how-do-i-use-the-follow-up-feature
This feature is not currently available for Outlook however.