uses 
  Mapi; 

function SendEMail(Handle: THandle; Mail: TStrings): Cardinal; 
type 
  TAttachAccessArray = array [0..0] of TMapiFileDesc; 
  PAttachAccessArray = ^TAttachAccessArray; 
var 
  MapiMessage: TMapiMessage; 
  Receip: TMapiRecipDesc; 
  Attachments: PAttachAccessArray; 
  AttachCount: Integer; 
  i1: integer; 
  FileName: string; 
  dwRet: Cardinal; 
  MAPI_Session: Cardinal; 
  WndList: Pointer; 
begin 
  dwRet := MapiLogon(Handle, 
    PChar(''), 
    PChar(''), 
    MAPI_LOGON_UI or MAPI_NEW_SESSION, 
    0, @MAPI_Session); 

  if (dwRet <> SUCCESS_SUCCESS) then 
  begin 
    MessageBox(Handle, 
      PChar('Error while trying to send email'), 
      PChar('Error'), 
      MB_ICONERROR or MB_OK); 
  end 
  else 
  begin 
    FillChar(MapiMessage, SizeOf(MapiMessage), #0); 
    Attachments := nil; 
    FillChar(Receip, SizeOf(Receip), #0); 

    if Mail.Values['to'] <> '' then 
    begin 
      Receip.ulReserved := 0; 
      Receip.ulRecipClass := MAPI_TO; 
      Receip.lpszName := StrNew(PChar(Mail.Values['to'])); 
      Receip.lpszAddress := StrNew(PChar('SMTP:' + Mail.Values['to'])); 
      Receip.ulEIDSize := 0; 
      MapiMessage.nRecipCount := 1; 
      MapiMessage.lpRecips := @Receip; 
    end; 

    AttachCount := 0; 

    for i1 := 0 to MaxInt do 
    begin 
      if Mail.Values['attachment' + IntToStr(i1)] = '' then 
        break; 
      Inc(AttachCount); 
    end; 

    if AttachCount > 0 then 
    begin 
      GetMem(Attachments, SizeOf(TMapiFileDesc) * AttachCount); 

      for i1 := 0 to AttachCount - 1 do 
      begin 
        FileName := Mail.Values['attachment' + IntToStr(i1)]; 
        Attachments[i1].ulReserved := 0; 
        Attachments[i1].flFlags := 0; 
        Attachments[i1].nPosition := ULONG($FFFFFFFF); 
        Attachments[i1].lpszPathName := StrNew(PChar(FileName)); 
        Attachments[i1].lpszFileName := 
          StrNew(PChar(ExtractFileName(FileName))); 
        Attachments[i1].lpFileType := nil; 
      end; 
      MapiMessage.nFileCount := AttachCount; 
      MapiMessage.lpFiles := @Attachments^; 
    end; 

    if Mail.Values['subject'] <> '' then 
      MapiMessage.lpszSubject := StrNew(PChar(Mail.Values['subject'])); 
    if Mail.Values['body'] <> '' then 
      MapiMessage.lpszNoteText := StrNew(PChar(Mail.Values['body'])); 

    WndList := DisableTaskWindows(0); 
    try 
    Result := MapiSendMail(MAPI_Session, Handle, 
      MapiMessage, MAPI_DIALOG, 0); 
    finally 
      EnableTaskWindows( WndList ); 
    end; 

    for i1 := 0 to AttachCount - 1 do 
    begin 
      StrDispose(Attachments[i1].lpszPathName); 
      StrDispose(Attachments[i1].lpszFileName); 
    end; 

    if Assigned(MapiMessage.lpszSubject) then 
      StrDispose(MapiMessage.lpszSubject); 
    if Assigned(MapiMessage.lpszNoteText) then 
      StrDispose(MapiMessage.lpszNoteText); 
    if Assigned(Receip.lpszAddress) then 
      StrDispose(Receip.lpszAddress); 
    if Assigned(Receip.lpszName) then 
      StrDispose(Receip.lpszName); 
    MapiLogOff(MAPI_Session, Handle, 0, 0); 
  end; 
end; 

procedure TForm1.Button1Click(Sender: TObject); 
var 
  mail: TStringList; 
begin 
  mail := TStringList.Create; 
  try 
    mail.values['to'] := 'Receiver-Email@test.xyz'; 
    mail.values['subject'] := 'Hello'; 
    mail.values['body'] := 'blah'; 
    mail.values['body'] := 'blah'; 
    mail.values['attachment0'] := 'C:\Test.txt'; 
    // mail.values['attachment1']:='C:\Test2.txt'; 
    sendEMail(Application.Handle, mail); 
  finally 
    mail.Free; 
  end; 
end;