Or perhaps you have forgotten to send an email?
Boomerang for Gmail solves those problems and more!
A free extension, available for Chrome, Safari and Firefox, Boomerang allows users to schedule emails to be sent at a later time and date. (So that angry email you emotionally typed can be reconsidered and softened when you are calm).
Boomerang improves efficiency as you can compose and schedule emails to be sent while you are away from your computer, send recurring emails, and track responses and read receipts.
Teachers, Boomerang means you don't have to spend the night before a field trip or special event with last minute reminders, you can compose the email and schedule to send or resend. Boomerang also will remind you if you fail to hear back from a recipient. This could help with scheduling conferences.
I recently to emailed someone who had their "out of office" reply on. Boomerang knew to ask me if I wanted to resend the email on the "return date" noted in their reply. When the return date arrived, Boomerang moved the email to the top of my priority box to remind me that I still needed to get in touch with that person.
There is a mobile version that is good for quick emails or reminders to yourself.
While there are some more extensive Boomerang offerings that cost money, they seem to be more related to business and promotional needs. I think most teachers will be very happy with the free version.
Please note when I first added Boomerang it did not appear in my Gmail immediately. Give it a few minutes to embed itself into your browser and Gmail.