--On Sunday, March 30, 2014 20:38 -0400 Ted Lemon
<ted(_dot_)lemon(_at_)nominum(_dot_)com> wrote:
On Mar 30, 2014, at 6:44 PM, John C Klensin
<john-ietf(_at_)jck(_dot_)com> wrote:
Whether one accepts it or not, "been here already" tests are
not about debugging. They are about loop detection and DoS
attacks.
Are there MTAs that make use of the Received: header for loop
detection?
It is long gone, but my recollection is that the
second-generation VM/CMS Internet-BITNET gateway did both count
and "been here" checks. Exim not only does a count check but
has a configuration parameter for the threshold count. Ned or
one of his group would be authoritative about their current
system and its PMDF predecessor but my recollection is that the
latter made at least one of those checks.
Based on the above, comments from others, and my general
impressions and recollections, I think the answer to the above
question is probably "yes, most of them".
john