Microsoft Outlook uses the Windows "long" date format to control some date formatting in the Calendar and Tasks. When the date format used in Outlook is not the desired date format, you can change it in the Control Panel, Regional settings.
If the screen width is too small to fit the date format, Outlook drops down to other formats.
To Change the Date format
- Open the control panel Regional and Language Settings applet (Region and Language in Windows 7 or Region in Windows 8).
- Choose the option to customize the settings. In Windows 7, click the Additional Settings button.
- Select the Date tab and change the long date format so that it includes the name of the day.
If your regional settings don't offer a long date format that includes the day of the week you can type a new format into the field. Use a format similar to dddd, MMMM dd, yyyy. The set of four d's represents the full week day name; use ddd for the abbreviated form.
Keep in mind that any change you make here will affect all Windows applications.
Tip: You can use any format you want as long as it contains valid notations and separators.