Knowledgebase

Follow the steps below to resolve this issue:

1. Ensure that all instances of PDF-XChange software, and your mail clients, are closed.

2. Open the Windows search, then enter 'regedit' and press Enter to launch the registry editor.

3. Enter the following string in the address bar:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail

4. Click the desired default mail client folder in the Mail dropdown:

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5. ​​Double-click the (Default) value in this key. The Edit String dialog box will open. Select the text in the Value data: text box, then and press Ctrl+C to copy it to the clipboard and click OK to close the dialog box.

6. Enter the following string in the address bar:

HKEY_CURRENT_USER\SOFTWARE\Clients

There should be a Mail key in the Clients key. If a Mail key is not present then right-click the Clients key, click New > key and enter Mail (case sensitive) as the name.

7. Click the Mail key, then double-click the Default key. The Edit String dialog box will open. Select the Value data: text box and press Ctrl+V to paste the clipboard content there:

8. Click OK.

The process is now complete. Please note that in some cases a system restart is required for this change to take effect.

This example is from a machine that has three mail clients installed. The relevant keys in relation to this issue are the (Default) and DLLPath keys. (Default) defines a name that can be used in other registry locations to refer to this client, and DLLPath is the path to the MAPI.DLL version the client will use.

There are two additional keys that are used to determine the client used as the default mail client for per-machine and per-user preferences. These are:

HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail and

HKEY_CURRENT_USER\SOFTWARE\Clients\Mail respectively.

The (Default) key should have a value that matches the name of an existing mail client. An example of a per-machine default mail client setting is detailed below:

The value of the (Default) key in this case is "Microsoft Outlook", and It matches the name defined for Microsoft Outlook in the Mail key of the Windows registry.

Similarly, a per-user default mail client can be set using HKEY_CURRENT_USER\SOFTWARE\Clients\Mail. As in the example above, the value of the (Default) key must match an existing mail client. An example of a per-user default mail client setting is detailed below:

  Note that it matches the definition in HKLM:

Summary

• Check that your desired mail client is correctly defined and can be found as a sub key of HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail.
• Check that your per-machine default contains a name that matches the name defined for your mail client.
• Check that your per-user default contains a name that matches the name defined for your mail client.
• Note that It is preferable to have no value as a default mail client rather than an invalid value.