Consider these requirements/instructions before you proceed with configuring Lotus Notes as a default mail client in the environment

1. This article assumes that the Notes on the Clients are installed on the same location, if that is not the case:
   1. Create Individual GPOs and assign them based on the requirement.
   2. Make sure you test these settings on a small set of computers before you deploy it to the whole domain as each domain is Unique.

Now that we understand and took care of certain important things, here is what you should do to get this going:

1. Start the Group Policy Management
2. Computer Configuration -> Preferences -> Windows Settings -> Registry
3. Add a New Registry Item
   1. Change the Action: to Replace
   2.  Set the hive TO HKEY_LOCAL_MACHINE
   3. SOFTWARE\Clients\Mail
   4. Check the Default Option
   5. Add the Value Data per your requirement.
      1. Lotus Notes (For Notes Clients Below Notes 9)
      2. IBM Notes (For Notes Clients Above Notes 9)
         1. optional values if you are configuring Outlook
            1. Microsoft Outlook
            2. Hotmail

4. Add a New Registry Item
   1. Change the Action: to Replace
   2.  Set the hive to HKEY_CLASSES_ROOT
   3. mailto
   4. Check the Default Option
   5. Add the Value Data:
      1. URL:mailto
5. Add a New Registry Item
   1. Change the Action: to Replace
   2.  Set the hive to HKEY_CLASSES_ROOT
   3. mailto
   4. Change  the Default Value to EditFlags
   5. Change  the Value Type to REG_DWord
   6. Add Value Data 2 as a HEX Value
6. Add a New Registry Item
   1. Change the Action: to Replace
   2. Set the hive to HKEY_CLASSES_ROOT
   3. mailto\DefaultIcon
   4. Check the Default Option
   5. Add the Value Data [Modify as required based on the environment]
      1. C:\Program Files (x86)\IBM\Lotus\Notes\notes.exe,0
         1. optional values if you are configuring Outlook
            1. “C:\Program Files\Microsoft Office\Office\outllib.dll”,-12
7. Add a New Registry Item
   1. Change the Action: to Replace
   2. Set the hive to HKEY_CLASSES_ROOT
   3. mailto\shell\open\command
   4. Check the Default Option
   5. Add the Value Data [Modify as required based on the environment]
      1. “C:\Program Files (x86)\IBM\Lotus\Notes\notes.exe”  -defini “%1”  [only for Notes]
         1. optional values if you are configuring Outlook
            1. “C:\Program Files\Microsoft Office\Office\outlook.exe” -c IPM.Note /m “%1” [only for Outlook]
8. Add a New Registry Item
   1. Change the Action: to Replace
   2. Set the hive to  HKEY_CURRENT_USER
   3. Software\Clients\mail
   4. Check the Default Option
   5. Add the Value Data per your requirement.
      1. Lotus Notes (For Notes Clients Below Notes 9)
      2. IBM Notes (For Notes Clients Above Notes 9)
         1. optional values if you are configuring Outlook
            1. Microsoft Outlook
            2. Hotmail