[exim] HELO and underscores - yet again - and an odd request

The arguments about underscores in HELO names have been well-rehearsed on
this list, and I don't want to go through them again. Suffice it to say
that _my_ current policy is to reject them, to make exceptions for a
limited period of time, but to (try to) insist that the other end clean up
their act.

As seems to happen every time, I now being told by the other end in my
latest dispute that "you are the only people we have this problem with",
and I need a way to convince them that we are not the only ones (though we
may well be the only ones they _currently_ have a problem with)

To that end, I'm making a somewhat odd request. Is there anyone out there
who

a) has the same basic policy - ie reject underscore in HELO
b) is prepared to have mail sent to them from this third party (and reject
it, obviously)

so that I can convince them that the problem is more widespread than they
think?

If so, please send me a suitable email address off-list, to
<Richard.Hall@???>
and I will be forever in your debt.

Many thanks,
Richard