[Exim] "CacheFlow Server" and exim4

There's a class of event which shows up in the logs as e.g

2002-12-07 00:42:43 H=(nric) [200.160.36.13] (CacheFlow Server)
F=<wvdvn@???> rejected RCPT...

Am I right in thinking that "CacheFlow Server" here is always
indicative of an open proxy? What actually _is_ this item of data in
the mainlog, I'm having a hard time finding it documented in chapter
44. I'm suspicious that it might be the rfc1413 "ident", but then why
isn't it prefixed with "U=" as indicated in 44.12?

Does anyone block mail on the basis of this indication, and if so,
could they offer an exim4 recipe for it, please? It seems to be quite
a pestilence.

cheers