[Rat]

Нашел на Delphimaster

Код:

function CheckAllowed(const s: string): boolean;
  var
    i: integer;
  begin
    Result:= false;
    for i:= 1 to Length(s) do
    begin
      if not (s[i] in ['a'..'z', 'A'..'Z', '0'..'9', '_', '-', '.']) then
        Exit;
    end;
    Result:= true;
  end;

function IsValidEmail(const Value: string): boolean;
var
  i: integer;
  namePart, serverPart: string;
begin
  Result:= false;
  i:= Pos('@', Value);
  if i = 0 then
    Exit;
  namePart:= Copy(Value, 1, i - 1);
  serverPart:= Copy(Value, i + 1, Length(Value));
  if (Length(namePart) = 0) or ((Length(serverPart) < 5)) then
    Exit;
  i:= Pos('.', serverPart);
  if (i = 0) or (i > (Length(serverPart) - 2)) then
    Exit;
  Result:= CheckAllowed(namePart) and CheckAllowed(serverPart);
end;