Boomerang is a Google Chrome extension that adds some powerful new features to Gmail!
Boomerang allows users to schedule emails to send at a later time, create follow ups for emails that they have not received responses from, and schedule reminders based off of emails they have received.
Get Boomerang here: www.boomeranggmail.com
Send An Email Later
With Boomerang, you can write an email now and schedule it to be sent automatically at a set time. Just write the messages as you normally would, then click the Send Later button. Use the calendar picker or the text box that understands language like "next Monday" to tell Boomerang when to send your message.
Follow Up On Emails
There are times you need to make sure you follow up within a specific time frame after sending a message. You can select to only be reminded if nobody replies, or regardless. This way you won't let messages slip through the crack and will never forget to follow up with people.
Set Reminders From Emails
Want a cleaner inbox, but don't want to lose track of important messages? Use Boomerang to take messages out of your inbox until you actually need them. Just click the Boomerang button when you have an email open, and choose when you need it again. Boomerang will archive your message and at the time you choose, bring it back to your inbox, marked unread, starred or even at the top of your message list.
Feature descriptions came from Boomerang's website.