Internet Explorer Client Registry Layout

Adding Client Applications
Internet Explorer uses the registry to determine which clients to use and how to use them. By changing the values that are stored in the registry for extended services such as mail and news, it is possible for Internet Explorer to launch applications that provide specialized Internet services.

Note In Windows 95 or later, Microsoft Windows NT 4.0, and Windows 2000 and later, the system registry contains the settings used by Internet Explorer to access the client services of other applications from within the browser. Internet Explorer establishes the default settings for these menu items during installation.
The Calendar, Contacts, Internet Call, Mail, and News registry settings can be found under the SOFTWARE\Clients subkey of HKEY_LOCAL_MACHINE.

Clients Subkey URL Protocol Description
Calendar Calendar and scheduling applications
Contacts ldap: Address book and contact database applications
Internet Call callto: Internet conference applications
Mail mailto: Internet e-mail and messaging clients
News news:, snews:, nntp: Internet newsgroup clients

For more information about predefined and pluggable protocols, and how to implement a protocol handler, see Asynchronous Pluggable Protocols.

Adding an Email Client Application
The following example demonstrates how to include a mail client application in the list of available applications. These steps are virtually identical for each of the Internet service application types listed above.

1.Create a new registry key for your Internet client application.
HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail\My_Mail_Client

2.Define the client application to be launched by Internet Explorer.

My_Mail_Client
(Default) = My Mail Client Name
shell
open
command
(Default) = "%ProgramFiles%\MyMail\MyMailClient.EXE"
Note The standard ShellExecute rules for registry keys apply; the ddeexec subkey may also be used to open the application using a running dde service.
3.Define the URL Protocol handlers implemented by this application.

My_Mail_Client
Protocols
mailto
(Default) = URL:MailTo Protocol
URL Protocol = ""
DefaultIcon
(Default) = "%ProgramFiles%\MyMail\MyMailClient.EXE",-3
shell
open
command
(Default) = "%ProgramFiles%\MyMail\MyMailClient.EXE" /mail "%1"
4.(Optional) List the file types and extensions recognized by your application.

My_Mail_Client
Protocols
.mymsg
(Default) = msg_file
Content Type = message/rfc822
msg_file
(Default) = Internet Email Message
DefaultIcon
(Default) = "%ProgramFiles%\MyMail\MyMailClient.EXE",-7
shell
open
command
(Default) = "%ProgramFiles%\MyMail\MyMailClient.EXE" /open "%1"
5.For e-mail client applications only, register a DLL (or executable) for handling the Simple MAPI calls needed by the Page by E-mail and Link by E-mail commands under the Send sub-menu of the File menu.

My_Mail_Client
DLLPath = C:\Program Files\MyMail\SimpleMAPI.dll
Note If the DLL Path value is present and the mail client has been selected as default, the DLL or EXE will be used. If the key is not present, the DLL or EXE associated with the CMCDLLName32 name/value pair in the [Mail] section of the Win.ini file will be used. If the Win.ini entry is not present, Mapi32.dll will be used.
6.(Optional) Set the new entry as the default e-mail client application.

HKEY_LOCAL_MACHINE
SOFTWARE
Clients
Mail
(Default) = My_Mail_Client
Once the registry is modified to include the new mail client application, Internet Explorer adds "My Mail Client Name" to the drop-down list of available e-mail applications. From this list, users can specify the mail client they want to be their default e-mail application. When the user selects the New Message item from the File menu, or one of the menu items available from the Mail toolbar button, Internet Explorer launches the application that the user has specified.

For additional information on how to register a browser, e-mail, media playback, or instant messaging program in the Windows registry, see Registering Programs with Client Types.

Adding HTML Editors
The steps for adding HTML editors to the drop-down list on the Programs tab of the Internet Options dialog box in Internet Explorer 5 and later are slightly different than the steps for adding client applications like mail and news.

1.Register the HTML editor in the OpenWithList file type association of .htm files.

HKEY_CLASSSES_ROOT
.htm
OpenWithList
MyEditor.exe
2.Add shell, edit, and command subkeys to the editor's HKEY_CLASSES_ROOT\Applications registry entry. The "%1" parameter refers to the file name of the active Web page.

HKEY_CLASSES_ROOT or HKEY_CURRENT_USER
Applications
MyEditor.exe
shell
edit
FriendlyAppName = My HTML Editor
command
(Default) = "%ProgramFiles%\MyHTML\MyEditor.exe" "%1"
Note The edit subkey is required. If the FriendlyAppName value is missing, the application itself is queried for this information.
Close and reopen the browser for these changes to take effect.

Setting the Default HTML Editor
In Internet Explorer 5 or later, whenever the HTML editor is selected from the drop-down list on the Programs tab of the Internet Options dialog box, the Edit with... command on the File menu is updated to reflect the selection.


HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER
Software
Microsoft
Internet Explorer
Default HTML Editor
Description = My HTML Editor
shell
edit
command
(Default) = "%ProgramFiles%\MyHTML\MyEditor.exe" "%1"
Note Applications such as FrontPage check this key to determine if they are registered as the default HTML editor.
Selecting a View Source Editor
By default when you use the View Source feature of Internet Explorer it launches Notepad as the text editor. The following registry key will allow another source editor to be used:


HKEY_LOCAL_MACHINE
Software
Microsoft
Internet Explorer
View Source Editor
Editor Name
(Default) = C:\Program Files\MyHTML\MyEditor.exe
Note Changes to this registry value take effect immediately. No environment variables (such as %ProgramFiles%) or command line arguments are allowed. The filename of the cached HTML file is passed as the first argument on the command line.
Note The View Source Editor key is not present in Internet Explorer 7 by default and will need to be created.