MSO could possibly stand for “Microsoft Office” and this is more likely because files with an MSO file extension are primarily associated with Microsoft Word, an application that is part of the Microsoft Office Suite and was developed by the Microsoft Corporation. MSO files usually contain important information for the proper rendering of HTML messages sent with an attached Microsoft Office file. This information will make sure that the attached file will be retrieved in the same content and format.
When a user attaches a Microsoft Office document in an HTML message, the message is sent as an MS Outlook HTML message and not a Microsoft Office Envelope message. This means that there must be an MSO file that would contain the necessary information to properly deliver the attached Microsoft Office document in the original program than it was created. Users might as well not open this file using a text editor as they couldn’t any useful information in the file when they open it with such and they can’t modify the file as well. Users who received this file with a secured and known attachment must not delete this file as well because doing so would only make the attached file useless and unusable.
If an MSO file is sent with a Microsoft Word 2000 attachment, it usually takes the file name “Oledata.MSO”. The file Oledata.MSO will be in a “background” mode in computers that have Microsoft Outlook 2000 or higher version installed; it will appear as a separate file attachment otherwise. Thus, the only program that can really open an MSO file is Microsoft Outlook, version 2010 or higher (if exists) for Windows and version 2011 for Mac OS.