[exim] More intelligent mail loop detection

Currently mail loop detection is done by a simple count of received headers. We have a situation where we receive mails with surprisingly large numbers of received headers, for reasons that are not entirely clear, but which involve the same mail server adding received headers repeatedly with no other hosts involved, i.e. "Received: from SERVER002.example.com ([1.2.3.4) by SERVER002.example.com; Tue, 08 May 2007 19:00:10 +0100".

By the time it reached us it's broken out of the loop, but we bounce it. Would it be difficult to have a check whether we've received it before, so if it's the first time it's got to us we don't bounce it, no matter how many received headers it has?

The obvious complication is that we have more than one mail server, so we would need a way of telling it which mail servers are ours.

Neil Youngman