If you have a reason that you want an email delivered later (I'm trying hard to think why you would need this feature) then Hit Me Later can do it. Just forward the email to XX@hitmelater.com (substitute hours for XX) and Hit Me Later will shoot the original email back to you when you specified. If you place a day in place of the XX, it will be sent to you on that day.
The best part? It's free.
Intentionally Delaying Your Email
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Write An Email To The Future You
Throw Away Email Account
Lingo 2.0: Bacn