Re: [exim] NUL characters are not allowed

>Date: Wed, 13 Oct 2004 08:20:44 -0700
>From: Jack Ziegler <ziegler@???>
>To: exim-users@???
>Subject: [exim] NUL characters are not allowed
>
>We're having problems with a handful of sites that reject messages
>with a 550 error, and the explanation "NUL characters are not
>allowed". I know that RFC 2822 specifies that a conformant
>receiver must accept messages with NUL, even though NUL is no
>longer allowed. What's most irritating is that the problem tends
>to happen on replies to messages that actually originated on
>another machine at the site that's rejecting the message. The
>offending NUL appears in quoted text from the original message.

Possibly the rejections are coming from the Cyrus IMAP server
which is known to reject NUL characters.

>Unfortunately, one of the people affected is the campus CIO, so I'm
>making an effort to find a local workaround.
>
>Exim version is 4.30 with exiscan-acl patch.

Exim 4.40 and later includes the expansion variable $body_zerocount
so you could trap such messages in an acl_smtp_data ACL and
reject them there. Ie before you attempt to deliver them to the
complaining site(s).

Alternatively you could use a transport filter:

transport_filter = /usr/bin/tr -d \\000

and strip them out before you pass them on to the complaining
site(s). This was suggested by Chris Edwards, Glasgow University
Computing Service, on this mailing list.

It's your call, but I'd be rather cautious about modifying messages
in transit.