You can use a rule to delay sending of all messages by pre-determined periods of time.
1.On the Tools menu, click Rules and Alerts, and then click New Rule.
2.Select Start from a blank rule.
3.In the Step 1: Select when messages should be checked box, click Check messages after sending, and then click Next.
4.In the Step 1: Select condition(s) list, select any options you want, and then click Next. If you do not select any check boxes, a confirmation dialog box appears. Clicking Yes applies this rule to all messages you send.
5.In the Step 1: Select action(s) list, select defer delivery by a number of minutes. Delivery can be delayed up to two hours.
6.In the Step 2: Edit the rule description (click on an underlined value) box, click the underlined phrase a number of and enter the number of minutes you want messages held before sending.
7.Click OK, and then click Next.
8.Select any exceptions, and then click Next.
9.In the Step 1: Specify a name for this rule box, type a name for the rule.
This applies to Outlook 2010, 2007, and 2003 that I know of.