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You see a file with the extension of.wmz when you receive a message with Oledata.mso attachment
Content provided by Microsoft
Applies to: Microsoft Outlook 2000 Standard Edition
When you receive a mail message you get an additional attachment, Oledata.mso. Eudora users may see a file with the extension of .wmz along with the inline file attachment. This file can not be opened or edited.
You are opening a mail message that has an inline attachment created with Microsoft Word 2000, the default mail format was set to HTML on the sending computer, and you are not using Outlook 2000 to view the message.
When sending HTML messages with an attached Microsoft Office 2000 document, the message is sent as an Outlook HTML message, not an Office Envelope message. The Oledata.mso file contains necessary information to properly render the attachment in the message in its originating program. This is known as "round tripping." There is no useful information for the user in this file and it is not editable. Do not delete this file; doing so could render the attached file unuseable.
If an HTML message is opened on a computer that does not have Outlook 2000 installed, you will see the Oledata.mso file as an additional attachment.