This might be more appropriate for exim-dev, but I'll start here.
I'm working on drafting a Best Current Practices RFC for MTA behaviours beyond what the basic message format RFCs require (RFC5322 in particular). I've already queried what Sendmail, postfix and a few commercial MTAs do in some specific cases, and I'm curious to know what exim does so I can add its data to the survey.
The two cases that have been most interesting so far are:
--
From: foo@bar
To: baz@blivit
This is not a header field
Subject: ha ha I fooled you
Date: Fri, 22 Oct 2010 11:08:22 -0700
This is where the body is
--
...and
--
From: foo@bar
To: baz@blivit
MIME-Version : 1.0
Subject: did you notice that extra space?
Date: Fri, 22 Oct 2010 11:08:22 -0700
This is where the body is
--
Obviously the issue has to do with how exim handles the two malformations found on the third line of each; in the first case it's not a valid header field line, and in the second case there's a space before the colon following the header field name.
I could try this myself with an exim installation someplace but that might not reveal other logic that my tests don't activate, so I thought it better to query people with more intimate knowledge of exim's internals.
