MSO File Extension

What is MSO file?

File with MSO extension contains data related to email attachment send with Microsoft Outook email client in the form of a MS Office 2000 document, typically generated by Microsoft Word. Information in MSO file allow user to open the attachment as a part of email message as a inline HTML document.

MSO files are typically named Oledata.mso and are not visible the both sender and receiver of the message, given that they use Outlook for email. If not, MSO file will be seen as a standard email attachment, and the document file will also be treated as a attachment file. A attachment named header.html, which contains message header, will also be present. MSO don’t hold any information useful to the users and should not be opened manually.

Programs which support MSO file extension

The list that follows enumerates programs compatible with MSO files, divided into 2 categories based on operating system on which they are available. Files with MSO suffix can be copied to any mobile device or system platform, but it may not be possible to open them properly on target system.

Updated: 03/14/2024

How to open file with MSO extension?

There can be multiple causes why you have problems with opening MSO files on given system. What is important, all common issues related to files with MSO extension can be resolved by the users themselves. The process is quick and doesn’t involve an IT expert. The list below will guide you through the process of addressing the encountered problem.

Step 1. Download and install Microsoft Outlook

The most common reason for such problems is the lack of proper applications that supports MSO files installed on the system. This issue can be addressed by downloading and installing Microsoft Outlook or different compatible program, such as Microsoft Organization Chart. On the top of the page a list that contains all programs grouped based on operating systems supported can be found. The safest method of downloading Microsoft Outlook installed is by going to developer’s website (Microsoft Corporation) and downloading the software using provided links.

Step 2. Check the version of Microsoft Outlook and update if needed

If the problems with opening MSO files still occur even after installing Microsoft Outlook, it is possible that you have an outdated version of the software. Check the developer’s website whether a newer version of Microsoft Outlook is available. Sometimes software developers introduce new formats in place of that already supports along with newer versions of their applications. If you have an older version of Microsoft Outlook installed, it may not support MSO format. All of the file formats that were handled just fine by the previous versions of given program should be also possible to open using Microsoft Outlook.

Step 3. Set the default application to open MSO files to Microsoft Outlook

If the issue has not been solved in the previous step, you should associate MSO files with latest version of Microsoft Outlook you have installed on your device. The next step should pose no problems. The procedure is straightforward and largely system-independent

Selecting the first-choice application in Windows

• Right-click the MSO file and choose Open with option
• Select Choose another app → More apps
• Finally select Look for another app on this PC, point to the folder where Microsoft Outlook is installed, check the Always use this app to open MSO files box and conform your selection by clicking OK button

Selecting the first-choice application in Mac OS

• By clicking right mouse button on the selected MSO file open the file menu and choose Information
• Open the Open with section by clicking its name
• From the list choose the appropriate program and confirm by clicking Change for all....
• If you followed the previous steps a message should appear: This change will be applied to all files with MSO extension. Next, click the Continue button to finalize the process.

Step 4. Check the MSO for errors

Should the problem still occur after following steps 1-3, check if the MSO file is valid. It is probable that the file is corrupted and thus cannot be accessed.

1. The MSO may be infected with malware – make sure to scan it with an antivirus tool.

If the file is infected, the malware that resides in the MSO file hinders attempts to open it. Scan the MSO file as well as your computer for malware or viruses. MSO file is infected with malware? Follow the steps suggested by your antivirus software.

2. Verify that the MSO file’s structure is intact

If the MSO file was sent to you by someone else, ask this person to resend the file to you. During the copy process of the file errors may occurred rendering the file incomplete or corrupted. This could be the source of encountered problems with the file. When downloading the file with MSO extension from the internet an error may occurred resulting in incomplete file. Try downloading the file again.

3. Ensure that you have appropriate access rights

Sometimes in order to access files user need to have administrative privileges. Log out of your current account and log in to an account with sufficient access privileges. Then open the Inline E-mail Attachment file.

4. Make sure that the system has sufficient resources to run Microsoft Outlook

The operating systems may note enough free resources to run the application that support MSO files. Close all running programs and try opening the MSO file.

5. Verify that your operating system and drivers are up to date

Regularly updated system, drivers, and programs keep your computer secure. This may also prevent problems with Inline E-mail Attachment files. Outdated drivers or software may have caused the inability to use a peripheral device needed to handle MSO files.

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