.mso files (oledata.mso) - how to open

This was a question a while back, that never got properly answered.

Answer is, don't worry about it. It's an e-mail attachment generated by old versions of Outlook (e.g. Office 2000) when files were attached to e-mails under certain conditions. Basically, oledata.mso contains instructions to the e-mail client about how to handle the attachments. The attachments themselves should be readable by the appropriate application. Don't delete it if you want to keep the attachments as attachments, rather than downloading them, but don't bother trying to make sense of it.