Código Delphi [-]
procedure TForm1.btnConnectClick(Sender: TObject);
var

  SMTP: TIdSMTP;
  Mail: TIdMessage;


begin

IdSMTP_SendMail := TIdSMTP.Create(Self);

with IdSMTP_SendMail do begin
IoHandler:=SSLIOHandler;
AuthType := satDefault;
Host := 'smtp.gmail.com';
port := 465 ;
useTLS:=utUseExplicitTLS;
Username := mi_cuenta;
Password := mi_password;
end;

mail := TIdMessage.Create(Self);
with mail do begin
From.Address := mi_cuenta;
Recipients.EMailAddresses := cuenta_del_destinatario;
Subject := 'Hola';
body.Text := 'Esto es una prueba';
end;


IdSMTP_SendMail.Connect;


IdSMTP_SendMail.Send(mail);

end;

Código Delphi [-]
procedure TfrmPrincipal.btnEnviarEmailClick(Sender: TObject);
begin
  with IdMessage do
  begin
    Body.Clear();
    Recipients.Clear();
    Sender.Address := edEmailRemitente.Text;
    Recipients.EMailAddresses := edEmailDestinatario.Text;
    Subject := edAsuntoEmail.Text;
    Body.AddStrings(mCuerpoEmail.Lines);
  end;

  with IdSMTP do
  begin
    IOHandler := IdSSLIOHandlerSocket;
    IdSSLIOHandlerSocket.SSLOptions.Method := sslvSSLv23; // sslv : SSLv2, SSLv3, TLSv1, SSLv23.
    IdSSLIOHandlerSocket.SSLOptions.Mode := sslmUnassigned;
    IdSSLIOHandlerSocket.SSLOptions.VerifyMode := [];
    IdSSLIOHandlerSocket.SSLOptions.VerifyDepth := 0;
    Port := 465;
    Host := edServidorSmtp.Text;
    AuthenticationType := atLogin;
    Username := edNombreUsuario.Text;
    Password := edContrasenaUsuario.Text;
    try
       Connect(5000);
    except
       ShowMessage('Error de conexión');
    end;

    btnEnviarEmail.Enabled := false;
    try
      Send(IdMessage);
      ShowMessage('Correo enviado con éxito');
    finally
      btnEnviarEmail.Enabled := true;
    end;

    if Connected then
      Disconnect();
  end;
end;

Código Delphi [-]
AuthType := satSASL;