[exim] Deny crappy HELO

Hello List!

I'd like to reject some spam based on HELO, but they are always changing and
i't difficult to set up a regex match.

Received: from [88.155.132.225] (helo=ELAD)
Received: from [89.48.167.77] (helo=familie-f79sok3)
Received: from [74.134.154.185] (helo=YOUR-XHTR8HVC4P)
Received: from [88.233.131.233] (helo=MAHMUT-5PWGUGKA)
Received: from [89.56.177.0] (helo=ina-vdadf88p3oh)

In the above examples the only the thing that is in common, that none of
them have any "." in the HELO. Is there a way to find them with regex?