According to
Microsoft this is a known problem with Outlook Express.
To work around this issue, follow these steps:
- Start Outlook Express.
- On the Tools menu, point to Message Rules, and then click Mail.
- In the Select the Conditions for your rule box, click to select the Where the message size is more than size check box.
- Click the size link in "Where the message size is more than size" in the Rule Description (click on an underlined value to edit it) box.
- In the Set size dialog box, type 1000, and then click OK.
- In the Select the Actions for your rule box, click to select the Delete it check box, and then click OK.
- Restart Outlook Express.