What is msimn.exe?

The .exe extension on a filename indicates an executable file. Executable files may, in some cases, harm your computer. Therefore, please read below to decide for yourself whether the msimn.exe on your computer is a Trojan that you should remove, or whether it is a file belonging to the Windows operating system or to a trusted application.

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Msimn.exe file information

Windows Task Manager with msimn
Msimn.exe process in Windows Task Manager

The process known as Outlook Express belongs to software Microsoft Windows Operating System by Microsoft (

Description: Msimn.exe is an important part of Windows, but often causes problems. Msimn.exe is located in a subfolder of "C:\Program Files"—generally C:\Program Files\Outlook Express\. Known file sizes on Windows 10/8/7/XP are 60,416 bytes (80% of all occurrences), 60,928 bytes, 71,680 bytes or 89,600 bytes. 
The file is a Microsoft signed file. The program uses ports to connect to or from a LAN or the Internet. Therefore the technical security rating is 7% dangerous; however you should also read the user reviews.

Uninstalling this variant: If you run into problems with msimn.exe, you may want to completely remove reFX Nexus (Control Panel ⇒ Uninstall a Program).

Recommended: Identify msimn.exe related errors

Important: Some malware camouflages itself as msimn.exe, particularly when located in the C:\Windows or C:\Windows\System32 folder. Therefore, you should check the msimn.exe process on your PC to see if it is a threat. We recommend Security Task Manager for verifying your computer's security. This was one of the Top Download Picks of The Washington Post and PC World.


User Comments

File msimn.exe is the main executable for Microsoft Outlook Express, which is an email and news group client that is installed with the Windows Operating system. Be sure to always check whether you have installed the latest updates since many worm viruses are exploiting this program to infect your system
It is an extension of Outlook. Used for playing sound from your outlook e-mails.
it would not download - XP microsoft update of security patch - error#oX3F5?
  Ann G.  
uses 100% of my CPU capacity
caused all my user name, passwords boxes to automatically fill with -----------------------
part of Outlook Express
Sometimes oulook express gets stuck downloading an email and closing outlook express and reopening it will not resolve the problem. You must go to webmail and deleting the offending email (for example 7 of 12) and then reopen outlook express. If it still does not resolve the problem you must reboot so it stops trying to "complete the download of the bad message". Well, the reboot is not necessary. Just go to the task manager, processes tab and "end process" the msmin.exe file. This is what is stuck. A reboot also clears it but is very time consuming.
uses 98% of my cpu
all I know is my outlook will not load until I shut this off on task manager
Part of Outlook Express 6

Rating chart

Summary: Average user rating of msimn.exe: based on 17 votes with 10 user comments. 7 users think msimn.exe is essential for Windows or an installed application. 4 users think it's probably harmless. One user thinks it's neither essential nor dangerous. 3 users suspect danger. 2 users think msimn.exe is dangerous and recommend removing it. One user is not sure about it.

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Best practices for resolving msimn issues

A clean and tidy computer is the key requirement for avoiding problems with msimn. This means running a scan for malware, cleaning your hard drive using cleanmgr and sfc /scannow, uninstalling programs that you no longer need, checking for Autostart programs (using msconfig) and enabling Windows' Automatic Update. Always remember to perform periodic backups, or at least to set restore points.

Should you experience an actual problem, try to recall the last thing you did, or the last thing you installed before the problem appeared for the first time. Use the resmon command to identify the processes that are causing your problem. Even for serious problems, rather than reinstalling Windows, you are better off repairing of your installation or, for Windows 8 and later versions, executing the DISM.exe /Online /Cleanup-image /Restorehealth command. This allows you to repair the operating system without losing data.

To help you analyze the msimn.exe process on your computer, the following programs have proven to be helpful: Security Task Manager displays all running Windows tasks, including embedded hidden processes, such as keyboard and browser monitoring or Autostart entries. A unique security risk rating indicates the likelihood of the process being potential spyware, malware or a Trojan. Malwarebytes Anti-Malware detects and removes sleeping spyware, adware, Trojans, keyloggers, malware and trackers from your hard drive.

Other processes

msimn.exe [all]