RE: [exim] Exim rejects: syntactically invalid argument

On Tue, 27 Sep 2005, Herb Martin wrote:

> What is the thinking on "helo_allow_chars = _" --
> other than "I want to receive their email" is there
> a reason to accept or reject such?

It's purpose is to allow certain exceptions (like _) to the RFC allowed
helo characters.

This was you can allow _ but still disallow other prohibited characters
that are usually the hallmark of spamware.