Microsoft Outlook oledata.mso attachment file

[NoeHuet]

Format name

No official name, could be "Microsoft Outlook oledata.mso attachment file"

Extensions

.mso

MIME/Media Type

application/octet-stream (mentionned in the Content-Type of EML part)

Description

This file format appears when attachments are extracted from emails produced using old versions of Microsoft Outlook, such as versions 2000 and Express 2004. In the original EML file, oledata.mso is a part declared as an attachment :
Content-Type: application/octet-stream; name=oledata.mso
Content-Transfer-Encoding: base64
Content-ID: <oledata.mso>
Content-Disposition: inline; filename="oledata.mso"
According to the Microsoft documentation page (see below), this part was used to correctly render Windows Metafile images (.WMZ) in Microsoft Outlook 2000. However, in the forums, I could see that it was used for other things, such as signatures and Office documents. The file content itself is neither structured nor intelligible.

Format type

Text

Vendor

Microsoft

File format identification signatures

• File is always entitled oledata.mso which is identifiable
• File always contains 00 at offsets 0x00 and 0x03 from BOF

Relevant links, documentation, extra information

• https://www.betaarchive.com/wiki/index.php/Microsoft_KB_Archive/222330
• https://learn.microsoft.com/en-us/answers/questions/4513430/oledata-mso-being-sent-with-emails
• http://files.avanquest.com/file-extension-mso/

Credit

Archives nationales de France