Check out the Mandrill API it has scheduled emails:

https://mandrillapp.com/api/docs/messages.ruby.html#method=s...

send_at (string)

When this message should be sent as a UTC timestamp in YYYY-MM-DD HH:MM:SS format. If you specify a time in the past, the message will be sent immediately. An additional fee applies for scheduled email, and this feature is only available to accounts with a positive balance. Validation: datetime