[S.M.S.]

Yo utilizo la siguiente función que no recuerdo de donde la saqué, pero que funciona perfectamente con los ejemplos de jachguate y de roman

Código Delphi [-]
function ValidEmail(email: string): boolean;
   // Devuelve True si la dirección de email es válida
   const
     // Caracteres válidos en un "átomo"
     atom_chars = [#33..#255] - ['(', ')', '<', '>', '@', ',', ';', 
     ':', '\', '/', '"', '.', '[', ']', #127];
     // Caracteres válidos en una "cadena-entrecomillada"
     quoted_string_chars = [#0..#255] - ['"', #13, '\'];
     // Caracteres válidos en un subdominio
     letters = ['A'..'Z', 'a'..'z'];
     letters_digits = ['0'..'9', 'A'..'Z', 'a'..'z'];
     subdomain_chars = ['-', '0'..'9', 'A'..'Z', 'a'..'z'];
   type
     States = (STATE_BEGIN, STATE_ATOM, STATE_QTEXT,
     STATE_QCHAR, STATE_QUOTE, STATE_LOCAL_PERIOD,
     STATE_EXPECTING_SUBDOMAIN, STATE_SUBDOMAIN, STATE_HYPHEN);
   var
     State: States;
     i, n, subdomains: integer;
     c: char;
begin 
  State := STATE_BEGIN;
  n := Length(email); 
  i := 1;
  subdomains := 1; 
  while (i <= n) do 
    begin
      c := email[i];
      case State of 
         STATE_BEGIN: 
                  if c in atom_chars then
                  State := STATE_ATOM 
                  else if c = '"' then 
                  State := STATE_QTEXT
                  else break;
         STATE_ATOM:
                  if c = '@' then
                  State := STATE_EXPECTING_SUBDOMAIN
                  else if c = '.' then 
                  State := STATE_LOCAL_PERIOD
                  else if not (c in atom_chars) then 
                  break; 
         STATE_QTEXT:
                  if c = '\' then
                  State := STATE_QCHAR 
                  else if c = '"' then
                  State := STATE_QUOTE 
                  else if not (c in quoted_string_chars) then 
                  break; 
         STATE_QCHAR:   
                  State := STATE_QTEXT; 
         STATE_QUOTE:
                  if c = '@' then 
                  State := STATE_EXPECTING_SUBDOMAIN
                  else if c = '.' then
                  State := STATE_LOCAL_PERIOD 
                  else break; 
         STATE_LOCAL_PERIOD:
                  if c in atom_chars then
                  State := STATE_ATOM 
                  else if c = '"' then 
                  State := STATE_QTEXT
                              else break; 
         STATE_EXPECTING_SUBDOMAIN: 
                  if c in letters then
                  State := STATE_SUBDOMAIN 
                  else break;
         STATE_SUBDOMAIN:
                  if c = '.' then
                  begin 
                      inc(subdomains);
                      State := STATE_EXPECTING_SUBDOMAIN
                  end
                  else if c = '-' then 
                  State := STATE_HYPHEN
                  else if not (c in letters_digits) then 
                  break;
         STATE_HYPHEN:
                  if c in letters_digits then
                  State := STATE_SUBDOMAIN
                  else if c <> '-' then break;
      end;
      inc(i);
    end;
  if i <= n then
  Result := False
  else
  Result := (State = STATE_SUBDOMAIN) and (subdomains >= 2);
end;

Saludos.