How can I send a mail message later? Back in the day, I remember having an e-mail program (perhaps it was Eudora?) that could schedule the sending of mail, so when composing a message, you could set some preference for when it would be sent. The message would be composed and queued up, but would not send until the computer was connected to the internet at or after the schedule time.

Is there a way to duplicate this feature in Apple Mail? Specifically, I want to compose a message, but rather than clicking "Send", I click "Delayed send" (either from the Services menu, the AppleScript menu, or, ideally, from an icon magically added to the Mail toolbar, but I don't expect that will be easy to pull ofF). When I do this, I'd get a dialog box asking me when I want to send the message. I enter the information, and the message is queued up and will be sent at the soonest time after the scheduled send time/date when the computer is on and connected.
It is possible to achieve this effect using Calendar and Automator:


Open Automator and create a Calendar Alarm.
Use the tasks “New mail message” and “Send Outgoing Messages”, customize them as required, and save (⌘S). 
An event will be created in Calendar automatically. Move the event to when you want the message to be sent.