A lot of Outlook issues are caused by various add-ins. So, disabling all add-ins is a useful step and should be the first step for Outlook troubleshooting.

 

Please note every add-in will be a subkey under the following subkeys.

 

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins

HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins

HKEY_LOCAL_MACHINE\Software\Microsoft\Exchange\Client\Extensions

HKEY_CURRENT_USER\Software\Microsoft\Exchange\Client\Extensions

 

So, to disable all add-ins thoroughly, we can follow the steps below.

 

1.    Click start -> Run… -> Type "regedit" (without quotation mark) and Click OK

2.    Locate the following subkey

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\Outlook\Addins

3.    Backup and Delete all subkeys under above subkey

4.    Repeat step 1-3 for the remain 3 subkeys

HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins

HKEY_LOCAL_MACHINE\Software\Microsoft\Exchange\Client\Extensions

HKEY_CURRENT_USER\Software\Microsoft\Exchange\Client\Extensions

 

Now, all add-ins are disabled. If the issue disappears, it means the root cause is a conflict between Outlook and some add-in. We can restore the registry back and delete them one by one to find out which one cause the issue.