Boomerang For Gmail

Boomerang for Gmail can schedule emails you send and postpone emails you've received.The former are sent reliably when desired and the latter disappear from your inbox to turn up again prominently at the preset time.
It's a pity Boomerang is not available for other email services as well and works only with Mozilla Firefox and Google Chrome.

Features

• Boomerang for Gmail is a browser extension to schedule emails for the future.
  You can pick future send times for emails and replies you send — until Jan 19, 2038.
• Boomerang understands some natural language {such as "5 min" or "next week"), and can pick a random time, too.
• Using Boomerang, you can also postpone messages you have received. They are archived until the desired time.
• When a postponed message re-appears, Boomerang can mark it unread, star it, and put it on top of the inbox.
• You can always find postponed messages under the "Boomerang" label. Messages scheduled for sending are in "Boomerang-Outbox".
• You do not have to be logged into Gmail or have it open for Boomerang to work.
• Boomerang for Gmail supports Mozilla Firefox and Google Chrome

You can get this from here.Boomerang For Gmail