Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

{ 
  Get names of installed Mail-Clients. 
  Namen der installierten Mail-Clients ermitteln. 
}

 uses
   Registry;

 function GetInstalledMailClients(AList: TStrings): Boolean;
 const
   RegClientsRoot = '\SOFTWARE\Clients';
   RegClientsMail = '\Mail';
   RegClientsOpenCmd = '\shell\open\command';
 var
   reg: TRegistry;
 begin
   Result := True;
   try
     AList.Clear;
     reg := nil;
     reg := TRegistry.Create;
     try
       with reg do
       begin
         CloseKey;
         RootKey := HKEY_LOCAL_MACHINE;
         if OpenKeyReadOnly(RegClientsroot + RegClientsMail) then
           if HasSubKeys then
             GetKeyNames(AList);
       end;
     finally
       if Assigned(reg) then reg.Free;
     end;
   except
     Result := False;
   end;
 end;

 procedure TForm1.Button1Click(Sender: TObject);
 begin
   GetInstalledMailClients(ListBox1.Items);
 end;