[Exim] NULL / filter

I'm wondering where we stand regarding NULLs in the message body ?? In
other words, characters with ascii value zero.

As I understand it, RFC 2822 specifically says this cannot appear in SMTP.
Nevertheless, exim is quite happy to pass messages containing NULLs
without modification. (a good thing imho, unlike some MTAs I could name)

However, bodies with NULLs seem to upset the message filter. For example,
on a system here (exim 3.35 on solaris 7) the test:

if $message_body matches "brown fox"

fails to match a message with body:

the <NULL> quick
brown fox

Note the NULL isn't even on the same line as the string to be matched.
Amongst other things, this explains why the gibe worms get through the
executable attachment filter.

I guess this is a grey area since the NULL is illegal.

Comments ?

Chris