Versions of Outlook prior to version 2007.

When creating a new message, replying to or forwarding an existing email message, after you have composed what you want to say, click on View and select Options instead of Send.

On the Delivery Options tab, enable the Do not deliver before option, then pick the date and time you want the email message to be sent.

Click on Close and then send the message. The email message Will be stored in your Outbox folder and Outlook will send it when the date and hour match the schedule.

If you are using Outlook 2007, it's even easier. When editing or composing an email message, click on Options and select Delay Delivery. Pick the time and date and select Close. Send the message and the message Will remain in your Outbox folder until the scheduled date and time.

If the aforementioned instructions do not work or you are looking for more robust email scheduling utilities, you can check out http://sendlater.4team.biz or http://www.mapilab.com/outlook/toolbox which seems to be much more flexible. We haven't used any of these items so we cannot speak to their suitibility.