-$Cambridge: exim/doc/doc-txt/NewStuff,v 1.114 2006/10/03 08:54:50 ph10 Exp $
+$Cambridge: exim/doc/doc-txt/NewStuff,v 1.115 2006/10/03 15:11:22 ph10 Exp $
New Features in Exim
--------------------
4. The variable $message_headers_raw provides a concatenation of all the
messages's headers without any decoding. This is in contrast to
- $message_headers, which does RFC2047 encoding on the header contents.
+ $message_headers, which does RFC2047 decoding on the header contents.
+
+5. In a DNS black list, when the facility for restricting the matching IP
+ values is used, the text from the TXT record that is set in $dnslist_text
+ may not reflect the true reason for rejection. This happens when lists are
+ merged and the IP address in the A record is used to distinguish them;
+ unfortunately there is only one TXT record. One way round this is not to use
+ merged lists, but that can be inefficient because it requires multiple DNS
+ lookups where one would do in the vast majority of cases when the host of
+ interest is not on any of the lists.
+
+ A less inefficient way of solving this problem has now been implemented. If
+ two domain names, comma-separated, are given, the second is used first to do
+ an initial check, making use of any IP value restrictions that are set. If
+ there is a match, the first domain is used, without any IP value
+ restrictions, to get the TXT record. As a byproduct of this, there is also a
+ check that the IP being tested is indeed on the first list. The first domain
+ is the one that is put in $dnslist_domain. For example:
+
+ reject message = rejected because $sender_ip_address is blacklisted \
+ at $dnslist_domain\n$dnslist_text
+ dnslists = sbl.spamhaus.org,sbl-xbl.spamhaus.org=127.0.0.2 : \
+ dul.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.10
+
+ For the first blacklist item, this starts by doing a lookup in
+ sbl-xbl.spamhaus.org and testing for a 127.0.0.2 return. If there is a
+ match, it then looks in sbl.spamhaus.org, without checking the return value,
+ and as long as something is found, it looks for the corresponding TXT
+ record. If there is no match in sbl-xbl.spamhaus.org, nothing more is done.
+ The second blacklist item is processed similarly.
+
+ If you are interested in more than one merged list, the same list must be
+ given several times, but because the results of the DNS lookups are cached,
+ the DNS calls themselves are not repeated. For example:
+
+ reject dnslists = http.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.2 : \
+ socks.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.3 : \
+ misc.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.4 : \
+ dul.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.10
+
+ In this case there is a lookup in dnsbl.sorbs.net, and if none of the IP
+ values matches (or if no record is found), this is the only lookup that is
+ done. Only if there is a match is one of the more specific lists consulted.
Version 4.63
git://git.exim.org / users / heiko / exim.git / blobdiff