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

function MailURLMayBeInvalid(const s: string): Boolean;
 var
   i: Integer;
   c: string;
 begin // ' ', a, o, u, ?, [, ], (, ), : in EMail-Address 
  Result := (Trim(s) = '') or (Pos(' ', AnsiLowerCase(s)) > 0) or
     (Pos('a', AnsiLowerCase(s)) > 0) or (Pos('o', AnsiLowerCase(s)) > 0) or
     (Pos('u', AnsiLowerCase(s)) > 0) or (Pos('?', AnsiLowerCase(s)) > 0) or
     (Pos('[', AnsiLowerCase(s)) > 0) or (Pos(']', AnsiLowerCase(s)) > 0) or
     (Pos('(', AnsiLowerCase(s)) > 0) or (Pos(')', AnsiLowerCase(s)) > 0) or
     (Pos(':', AnsiLowerCase(s)) > 0);
   if Result then Exit; // @ not in EMail-Address; 
  i      := Pos('@', s);
   Result := (i = 0) or (i = 1) or (i = Length(s));
   if Result then Exit;
   Result := (Pos('@', Copy(s, i + 1, Length(s) - 1)) > 0);
   if Result then Exit; // Domain <= 1 
  c      := Copy(s, i + 1, Length(s));
   Result := Length(c) <= 1;
   if Result then Exit;
   i      := Pos('.', c);
   Result := (i = 0) or (i = 1) or (i = Length(c));
 end;