Hey checkyourlogs.net fans!

I stumbled across an issue yesterday where the Mail settings app in Control Panel on my Windows 10 1903 PC wouldn’t open. In expected style, it provided a very non-helpful error “Application not found.” What do you mean, not found? This is the Control Panel for goodness sake!

Best guess is that an Office 365 App Update sometime previous “broke” my settings. Especially problematic since my Outlook O365 wouldn’t open because I needed to delete a corrupt profile using, you guessed it, my Control Panel Mail settings app. Oh well, enough ranting and raving, let’s get to the fix!

The Control Panel mail settings app is actually MLCFG32.CPL, located at C:\Program Files (x86)\Microsoft Office\root\Office16\MLCFG32.CPL in a typical Office 365 desktop installation. Quickly browsing to that folder location indicates my file is present and accounted for as expected.


One other app is necessary for my Control Panel Mail settings app to work: AppVLP.exe. It should exist at C:\Program Files (x86)\Microsoft Office\root\Client\ and a quick check proves it does.


With the files intact, my next check were the registry keys. On my Windows 10 PC with O365, there are six registry keys in use for the Control Panel Mail settings app. They are:

HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Classes\CLSID\{A0D4CD32-5D5D-4f72-BAAA-767A7AD6BAC5}\shell\open\command

HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Classes\CLSID\{A0D4CD32-5D5D-4f72-BAAA-767A7AD6BAC5}\DefaultIcon

HKEY_CLASSES_ROOT\WOW6432Node\CLSID\{A0D4CD32-5D5D-4f72-BAAA-767A7AD6BAC5}\DefaultIcon

HKEY_CLASSES_ROOT\WOW6432Node\CLSID\{A0D4CD32-5D5D-4f72-BAAA-767A7AD6BAC5}\shell\open\command

HKEY_CLASSES_ROOT\CLSID\{A0D4CD32-5D5D-4f72-BAAA-767A7AD6BAC5}\shell\open\command

HKEY_CLASSES_ROOT\CLSID\{A0D4CD32-5D5D-4f72-BAAA-767A7AD6BAC5}\DefaultIcon

Old school admins might prefer Regedit, which still works great. In this case I’m going to use PowerShell. PowerShell includes a Registry Provider and HKEY_LOCAL_MACHINE is already available as a PSDrive named HKLM. Before I can access HKEY_CLASSES_ROOT though, I must quickly configure a PSDrive for it using the cmdlet New-PSDrive.


With that done, I can now access HKEY_CLASSES_ROOT using the PSDrive named HKCR. I’ll check the current value of the each key using Get-ItemProperty. Checking the first key, my one-liner is

(Get-ItemProperty -LiteralPath "HKLM:\SOFTWARE\WOW6432Node\Classes\CLSID\{A0D4CD32-5D5D-4f72-BAAA-767A7AD6BAC5}\shell\open\command").'(default)'

Based on the folder paths we verified earlier, the value in this key should be “C:\Program Files (x86)\Microsoft Office\root\Client\AppVLP.exe” rundll32.exe shell32.dll,Control_RunDLL “C:\Program Files (x86)\Microsoft Office\root\Office16\MLCFG32.CPL.” Unfortunately, our results are a little different.


One problem found! Now I’ll fix it using the Set-ItemProperty cmdlet. My one-liner is

Set-ItemProperty -LiteralPath "HKLM:\SOFTWARE\WOW6432Node\Classes\CLSID\{A0D4CD32-5D5D-4f72-BAAA-767A7AD6BAC5}\shell\open\command"-name '(default)' -Value '"C:\Program Files (x86)\Microsoft Office\root\Client\AppVLP.exe" rundll32.exe shell32.dll,Control_RunDLL "C:\Program Files (x86)\Microsoft Office\root\Office16\MLCFG32.CPL"'


Now, run our Get-ItemProperty one-liner again to verify everything is right as rain.


Repeat this process for the other keys, ensuring data is entered meticulously. Once done, go into Control Panel and run the newly fixed Mail settings app!


You know me, I’m always looking for ways to make IT Pro Admin’s lives easier. If you want to automate the process and just get it fixed, I’ve created a script available from my GitHub repo here: https://github.com/JONeillSr/Set-MailCPL. The script reports if setting each key is successful or not.


Until next time checkyourlogs.net fans, enjoy your IT adventures!

John Sr.