я что то не понял твои параметры....

а вообще строка mailto:user@server.ru?subject=Моя Тема


и вот почитай внимательно

ShellExecute
Performs an operation on a specified file.



HINSTANCE ShellExecute(
HWND hwnd,
LPCTSTR lpVerb,
LPCTSTR lpFile,
LPCTSTR lpParameters,
LPCTSTR lpDirectory,
INT nShowCmd
);

Parameters
hwnd
Handle to a parent window. This window receives any message boxes that an application produces. For example, an application may report an error by producing a message box.
lpVerb
A string, referred to as a verb, that specifies the action to be performed. The set of available verbs depends on the particular file or folder. Generally, the actions available from an object's context menu are available verbs. For more information about verbs and their availability, see Object Verbs. See Extending Context Menus for further discussion of context menus. The following verbs are commonly used: Verb Description
edit Launches an editor and opens the document for editing. If lpFile is not a document file, the function will fail.
explore Explores the folder specified by lpFile.
find Initiates a search starting from the specified directory.
open Opens the file specified by the lpFile parameter. The file can be an executable file, a document file, or a folder.
print Prints the document file specified by lpFile. If lpFile is not a document file, the function will fail.
properties Displays the file or folder's properties.
If you set this paramater to NULL:

For systems prior to Microsoft® Windows® 2000, the default verb is used if it is valid and available in the registry. If not, the "open" verb is used.
For Windows 2000 and later systems, the default verb is used if available. If not, the "open" verb is used. If neither verb is available, the system uses the first verb listed in the registry.
lpFile
Address of a null-terminated string that specifies the file or object on which to execute the specified verb. To specify a shell namespace object, pass the fully-qualified parse name. Note that not all verbs are supported on all objects. For example, not all document types support the "print" verb.
lpParameters
If the lpFile parameter specifies an executable file, lpParameters is an address to a null-terminated string that specifies the parameters to be passed to the application.The format of this string is determined by the verb that is to be invoked. If lpFile specifies a document file, lpParameters should be NULL.
lpDirectory
Address of a null-terminated string that specifies the default directory.
nShowCmd
Flags that specify how an application is to be displayed when it is opened. If lpFile specifies a document file, the flag is simply passed to the associated application. It is up to the application to decide how to handle it.
SW_HIDE Hides the window and activates another window.
SW_MAXIMIZE Maximizes the specified window.
SW_MINIMIZE Minimizes the specified window and activates the next top-level window in the z-order.
SW_RESTORE Activates and displays the window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when restoring a minimized window.
SW_SHOW Activates the window and displays it in its current size and position.
SW_SHOWDEFAULT Sets the show state based on the SW_ flag specified in the STARTUPINFO structure passed to the CreateProcess function by the program that started the application. An application should call ShowWindow with this flag to set the initial show state of its main window.
SW_SHOWMAXIMIZED Activates the window and displays it as a maximized window.
SW_SHOWMINIMIZED Activates the window and displays it as a minimized window.
SW_SHOWMINNOACTIVE Displays the window as a minimized window. The active window remains active.
SW_SHOWNA Displays the window in its current state. The active window remains active.
SW_SHOWNOACTIVATE Displays a window in its most recent size and position. The active window remains active.
SW_SHOWNORMAL Activates and displays a window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when displaying the window for the first time.

Return Values
Returns a value greater than 32 if successful, or an error value that is less than or equal to 32 otherwise. The following table lists the error values. The return value is cast as an HINSTANCE for backward compatibility with 16-bit Microsoft® Windows® applications. It is not a true HINSTANCE, however. The only thing that can be done with the returned HINSTANCE is to cast it to an integer and compare it with the value 32 or one of the error codes below.

0 The operating system is out of memory or resources.
ERROR_FILE_NOT_FOUND The specified file was not found.
ERROR_PATH_NOT_FOUND The specified path was not found.
ERROR_BAD_FORMAT The .exe file is invalid (non-Win32® .exe or error in .exe image).
SE_ERR_ACCESSDENIED The operating system denied access to the specified file.
SE_ERR_ASSOCINCOMPLETE The file name association is incomplete or invalid.
SE_ERR_DDEBUSY The DDE transaction could not be completed because other DDE transactions were being processed.
SE_ERR_DDEFAIL The DDE transaction failed.
SE_ERR_DDETIMEOUT The DDE transaction could not be completed because the request timed out.
SE_ERR_DLLNOTFOUND The specified dynamic-link library was not found.
SE_ERR_FNF The specified file was not found.
SE_ERR_NOASSOC There is no application associated with the given file name extension. This error will also be returned if you attempt to print a file that is not printable.
SE_ERR_OOM There was not enough memory to complete the operation.
SE_ERR_PNF The specified path was not found.
SE_ERR_SHARE A sharing violation occurred.

Remarks
This method allows you to execute any commands in a folder's context menu or stored in the registry.

To open a folder, use either of the following calls:

ShellExecute(handle, NULL, path_to_folder, NULL, NULL, SW_SHOWNORMAL);

or

ShellExecute(handle, "open", path_to_folder, NULL, NULL, SW_SHOWNORMAL);

To explore a folder, use:

ShellExecute(handle, "explore", path_to_folder, NULL, NULL, SW_SHOWNORMAL);

To launch the shell's Find utility for a directory, use:

ShellExecute(handle, "find", path_to_folder, NULL, NULL, 0);

If lpOperation is NULL, the function opens the file specified by lpFile. If lpOperation is "open" or "explore", the function will attempt to open or explore the folder.

With multiple monitors, if you specify the window handle and set lpOperation to "Properties", any windows created by ShellExecute may not appear in the correct position.

To obtain information about the application that is launched as a result of calling ShellExecute, use ShellExecuteEx.

See Also
IShellExecuteHook

Requirements
Windows NT/2000: Requires Windows NT 3.1 or later.
Windows 95/98: Requires Windows 95 or later.
Header: Declared in shellapi.h.
Import Library: shell32.lib.

так в бате ж используеться готовый шаблон БАТА а не ненойми откуда.... точто есть там тело письма то ето зашито в бате.... да ты можешь себе сделать шаблон... и каким то чудом вызывать его... но а как другим.. и подумай, что если у кого то к примеру аутлук.. ???

никак нельзя ...... хотя.....