...  
   IdMsgSend.ContentType := 'text/plain';      
   IdMsgSend.CharSet := 'Windows-1251';   
   try
      idSMTP.Send(IdMsgSend);
   finally
      idSMTP.Disconnect;
   end;

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, IdBaseComponent, IdComponent, IdTCPConnection,
  IdTCPClient, IdMessageClient, IdSMTP, IdMessage;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;


implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
  LSMTP: TIdSMTP;
  LMsg: TIdMessage; I:integer;
  Year, Month, Day: Word;
begin
  LSMTP := TIdSMTP.Create(nil);
  LMsg := TIdMessage.Create(LSMTP);
  DecodeDate(Now, Year, Month, Day);
  with LMsg do begin
    Subject := 'MailTest at ' + IntToStr(Day) + IntToStr(Month) + IntToStr(Year);
    Recipients.EMailAddresses := 'address@mail.ru';
    From.Text := 'MailSender';
    ReplyTo.EMailAddresses:= 'reply@address.ru';
    Body.Text := 'Тест на ' + DateToStr(Now) + ' ' + TimeToStr(Now) + ' (English text)';
    CharSet:= 'Windows-1251';
    ContentType :='text/plain';
    Encoding:= meMIME;
//    ПОДКЛЮЧЕНИЕ АТАЧМЕНТА
//    TIdAttachment.Create(LMsg.MessageParts , 'c:\test.txt');
  end;

  with LSMTP do begin
    Host := 'host.ru'; // ВАШ ХОСТ SMTP
// ЕСЛИ К ХОСТУ ПОДКЛЮЧЕНИЕ ПО ЛОГИНУ И ПАРОЛЮ
    Username := 'user_name'; //ВАШ ЛОГИН!!!
    Password:= 'password'; // ВАШ ПАРОЛЬ!!!
    Connect;
    try
      Send(LMsg);
    finally
      ShowMessage('Сообщение отправлено.');
    end;
    Disconnect;
   end;
   FreeAndNil(LMsg);
   FreeAndNil(LSMTP);
end;
end.