Files with the extension MSO contain an inline e-mail attachment. This means that they contain a Microsoft Word 2000 document that was sent as an Outlook HTML message with Word. The file, which is mostly Oledata.Mso contains all the necessary data to correctly display the document within Outlook.
If the message is displayed on a system that does not have Outlook 2000 installed, the oledata.Mso file appears as an attachment.
The file can not be used or edited on its own and should not be deleted as this can make the corresponding message unreadable.
Most often resolving problems with opening MSO files is very simple. Just install an appropriate program that supports such files. All of the listed programs support MSO files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of MSO files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate MSO files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Outlook applications is not on the list, select "Browse" option in order to manually locate the directory where Outlook has been installed.
Sometimes problems with opening MSO files may not lie with the application itself, but can arise due to other causes, such as: