-$Cambridge: exim/doc/doc-txt/NewStuff,v 1.39 2005/05/03 14:20:00 ph10 Exp $
+$Cambridge: exim/doc/doc-txt/NewStuff,v 1.56 2005/07/27 18:27:55 fanf2 Exp $
New Features in Exim
--------------------
updated when there is a relatively large batch of changes). The doc/ChangeLog
file contains a listing of all changes, including bug fixes.
+Exim version 4.53
+-----------------
+
+TK/01 Added the "success_on_redirect" address verification option. When an
+ address generates new addresses during routing, Exim will abort
+ verification with "success" when more than one address has been
+ generated, but continue to verify a single new address. The latter
+ does not happen when the new "success_on_redirect" option is set, like
+
+ require verify = recipient/success_on_redirect/callout=10s
+
+ In that case, verification will succeed when a router generates a new
+ address.
+
+
+Exim version 4.52
+-----------------
+
+TF/01 Support for checking Client SMTP Authorization has been added. CSA is a
+ system which allows a site to advertise which machines are and are not
+ permitted to send email. This is done by placing special SRV records in
+ the DNS, which are looked up using the client's HELO domain. At this
+ time CSA is still an Internet-Draft.
+
+ Client SMTP Authorization checks are performed by the ACL condition
+ verify=csa. This will fail if the client is not authorized. If there is
+ a DNS problem, or if no valid CSA SRV record is found, or if the client
+ is authorized, the condition succeeds. These three cases can be
+ distinguished using the expansion variable $csa_status, which can take
+ one of the values "fail", "defer", "unknown", or "ok". The condition
+ does not itself defer because that would be likely to cause problems
+ for legitimate email.
+
+ The error messages produced by the CSA code include slightly more
+ detail. If $csa_status is "defer" this may be because of problems
+ looking up the CSA SRV record, or problems looking up the CSA target
+ address record. There are four reasons for $csa_status being "fail":
+ the client's host name is explicitly not authorized; the client's IP
+ address does not match any of the CSA target IP addresses; the client's
+ host name is authorized but it has no valid target IP addresses (e.g.
+ the target's addresses are IPv6 and the client is using IPv4); or the
+ client's host name has no CSA SRV record but a parent domain has
+ asserted that all subdomains must be explicitly authorized.
+
+ The verify=csa condition can take an argument which is the domain to
+ use for the DNS query. The default is verify=csa/$sender_helo_name.
+
+ This implementation includes an extension to CSA. If the query domain
+ is an address literal such as [192.0.2.95], or if it is a bare IP
+ address, Exim will search for CSA SRV records in the reverse DNS as if
+ the HELO domain was e.g. 95.2.0.192.in-addr.arpa. Therefore it is
+ meaningful to say, for example, verify=csa/$sender_host_address - in
+ fact, this is the check that Exim performs if the client does not say
+ HELO. This extension can be turned off by setting the main
+ configuration option dns_csa_use_reverse = false.
+
+ If a CSA SRV record is not found for the domain itself, then a search
+ is performed through its parent domains for a record which might be
+ making assertions about subdomains. The maximum depth of this search is
+ limited using the main configuration option dns_csa_search_limit, which
+ takes the value 5 by default. Exim does not look for CSA SRV records in
+ a top level domain, so the default settings handle HELO domains as long
+ as seven (hostname.five.four.three.two.one.com) which encompasses the
+ vast majority of legitimate HELO domains.
+
+ The dnsdb lookup also has support for CSA. Although dnsdb already
+ supports SRV lookups, this is not sufficient because of the extra
+ parent domain search behaviour of CSA, and (as with PTR lookups)
+ dnsdb also turns IP addresses into lookups in the reverse DNS space.
+ The result of ${lookup dnsdb {csa=$sender_helo_name} } has two
+ space-separated fields: an authorization code and a target host name.
+ The authorization code can be "Y" for yes, "N" for no, "X" for explicit
+ authorization required but absent, or "?" for unknown.
+
+PH/01 The amount of output produced by the "make" process has been reduced,
+ because the compile lines are often rather long, making it all pretty
+ unreadable. The new style is along the lines of the 2.6 Linux kernel:
+ just a short line for each module that is being compiled or linked.
+ However, it is still possible to get the full output, by calling "make"
+ like this:
+
+ FULLECHO='' make -e
+
+ The value of FULLECHO defaults to "@", the flag character that suppresses
+ command reflection in "make". When you ask for the full output, it is
+ given in addition to the the short output.
+
+TF/02 There have been two changes concerned with submission mode:
+
+ Until now submission mode always left the return path alone, whereas
+ locally-submitted messages from untrusted users have the return path
+ fixed to the user's email address. Submission mode now fixes the return
+ path to the same address as is used to create the Sender: header. If
+ /sender_retain is specified then both the Sender: header and the return
+ path are left alone.
+
+ Note that the changes caused by submission mode take effect after the
+ predata ACL. This means that any sender checks performed before the
+ fix-ups will use the untrusted sender address specified by the user, not
+ the trusted sender address specified by submission mode. Although this
+ might be slightly unexpected, it does mean that you can configure ACL
+ checks to spot that a user is trying to spoof another's address, for
+ example.
+
+ There is also a new /name= option for submission mode which allows you
+ to specify the user's full name to be included in the Sender: header.
+ For example:
+
+ accept authenticated = *
+ control = submission/name=${lookup {$authenticated_id} \
+ lsearch {/etc/exim/namelist} }
+
+ The namelist file contains entries like
+
+ fanf: Tony Finch
+
+ And the resulting Sender: header looks like
+
+ Sender: Tony Finch <fanf@exim.org>
+
+TF/03 The control = fakereject ACL modifier now has a fakedefer counterpart,
+ which works in exactly the same way except it causes a fake SMTP 450
+ response after the message data instead of a fake SMTP 550 response.
+ You must take care when using fakedefer because it will cause messages
+ to be duplicated when the sender retries. Therefore you should not use
+ fakedefer if the message will be delivered normally.
+
+TF/04 There is a new ratelimit ACL condition which can be used to measure
+ and control the rate at which clients can send email. This is more
+ powerful than the existing smtp_ratelimit_* options, because those
+ options only control the rate of commands in a single SMTP session,
+ whereas the new ratelimit condition works across all connections
+ (concurrent and sequential) to the same host.
+
+ The syntax of the ratelimit condition is:
+
+ ratelimit = <m> / <p> / <options> / <key>
+
+ If the average client sending rate is less than m messages per time
+ period p then the condition is false, otherwise it is true.
+
+ The parameter p is the smoothing time constant, in the form of an Exim
+ time interval e.g. 8h for eight hours. A larger time constant means it
+ takes Exim longer to forget a client's past behaviour. The parameter m is
+ the maximum number of messages that a client can send in a fast burst. By
+ increasing both m and p but keeping m/p constant, you can allow a client
+ to send more messages in a burst without changing its overall sending
+ rate limit. Conversely, if m and p are both small then messages must be
+ sent at an even rate.
+
+ The key is used to look up the data used to calcluate the client's
+ average sending rate. This data is stored in a database maintained by
+ Exim in its spool directory alongside the retry database etc. For
+ example, you can limit the sending rate of each authenticated user,
+ independent of the computer they are sending from, by setting the key
+ to $authenticated_id. The default key is $sender_host_address.
+ Internally, Exim includes the smoothing constant p and the options in
+ the lookup key because they alter the meaning of the stored data.
+ This is not true for the limit m, so you can alter the configured
+ maximum rate and Exim will still remember clients' past behaviour,
+ but if you alter the other ratelimit parameters Exim will effectively
+ forget their past behaviour.
+
+ Each ratelimit condition can have up to two options. The first option
+ specifies what Exim measures the rate of, and the second specifies how
+ Exim handles excessively fast clients.
+
+ The per_mail option means that it measures the client's rate of sending
+ messages. This is the default if none of the per_* options is specified.
+
+ The per_conn option means that it measures the client's connection rate.
+
+ The per_byte option limits the sender's email bandwidth. Note that it
+ is best to use this option in the DATA ACL; if it is used in an earlier
+ ACL it relies on the SIZE parameter on the MAIL command, which may be
+ inaccurate or completely missing. You can follow the limit m in the
+ configuration with K, M, or G to specify limits in kilobytes,
+ megabytes, or gigabytes respectively.
+
+ The per_cmd option means that Exim recomputes the rate every time the
+ condition is processed, which can be used to limit the SMTP command rate.
+ The alias per_rcpt is provided for use in the RCPT ACL instead of per_cmd
+ to make it clear that the effect is to limit the rate at which recipients
+ are accepted. Note that in this case the rate limiting engine will see a
+ message with many recipients as a large high-speed burst.
+
+ If a client's average rate is greater than the maximum, the rate
+ limiting engine can react in two possible ways, depending on the
+ presence of the strict or leaky options. This is independent of the
+ other counter-measures (e.g. rejecting the message) that may be
+ specified by the rest of the ACL. The default mode is leaky, which
+ avoids a sender's over-aggressive retry rate preventing it from getting
+ any email through.
+
+ The strict option means that the client's recorded rate is always
+ updated. The effect of this is that Exim measures the client's average
+ rate of attempts to send email, which can be much higher than the
+ maximum. If the client is over the limit it will be subjected to
+ counter-measures until it slows down below the maximum rate.
+
+ The leaky option means that the client's recorded rate is not updated
+ if it is above the limit. The effect of this is that Exim measures the
+ client's average rate of successfully sent email, which cannot be
+ greater than the maximum. If the client is over the limit it will
+ suffer some counter-measures, but it will still be able to send email
+ at the configured maximum rate, whatever the rate of its attempts.
+
+ As a side-effect, the ratelimit condition will set the expansion
+ variables $sender_rate containing the client's computed rate,
+ $sender_rate_limit containing the configured value of m, and
+ $sender_rate_period containing the configured value of p.
+
+ Exim's other ACL facilities are used to define what counter-measures
+ are taken when the rate limit is exceeded. This might be anything from
+ logging a warning (e.g. while measuring existing sending rates in order
+ to define our policy), through time delays to slow down fast senders,
+ up to rejecting the message. For example,
+
+ # Log all senders' rates
+ warn
+ ratelimit = 0 / 1h / strict
+ log_message = \
+ Sender rate $sender_rate > $sender_rate_limit / $sender_rate_period
+
+ # Slow down fast senders
+ warn
+ ratelimit = 100 / 1h / per_rcpt / strict
+ delay = ${eval: 10 * ($sender_rate - $sender_rate_limit) }
+
+ # Keep authenticated users under control
+ deny
+ ratelimit = 100 / 1d / strict / $authenticated_id
+
+ # System-wide rate limit
+ defer
+ message = Sorry, too busy. Try again later.
+ ratelimit = 10 / 1s / $primary_hostname
+
+ # Restrict incoming rate from each host, with a default rate limit
+ # set using a macro and special cases looked up in a table.
+ defer
+ message = Sender rate $sender_rate exceeds \
+ $sender_rate_limit messages per $sender_rate_period
+ ratelimit = ${lookup {$sender_host_address} \
+ cdb {DB/ratelimits.cdb} \
+ {$value} {RATELIMIT} }
+
+ Warning: if you have a busy server with a lot of ratelimit tests,
+ especially with the per_rcpt option, you may suffer from a performance
+ bottleneck caused by locking on the ratelimit hints database. Apart from
+ making your ACLs less complicated, you can reduce the problem by using a
+ RAM disk for Exim's hints directory, /var/spool/exim/db/. However this
+ means that Exim will lose its hints data after a reboot (including retry
+ hints, the callout cache, and ratelimit data).
+
+TK/01 Added an 'spf' lookup type that will return an SPF result for a given
+ email address (the key) and an IP address (the database):
+
+ ${lookup {tom@duncanthrax.net} spf{217.115.139.137}}
+
+ The lookup will return the same result strings as they can appear in
+ $spf_result (pass,fail,softfail,neutral,none,err_perm,err_temp). The
+ lookup is armored in EXPERIMENTAL_SPF. Currently, only IPv4 addresses
+ are supported.
+
+ Patch submitted by Chris Webb <chris@arachsys.com>.
+
+PH/02 There's a new verify callout option, "fullpostmaster", which first acts
+ as "postmaster" and checks the recipient <postmaster@domain>. If that
+ fails, it tries just <postmaster>, without a domain, in accordance with
+ the specification in RFC 2821.
+
+PH/03 The action of the auto_thaw option has been changed. It no longer applies
+ to frozen bounce messages.
+
+TK/02 There are two new expansion items to help with the implementation of
+ the BATV "prvs" scheme in an Exim configuration:
+
+
+ ${prvs {<ADDRESS>}{<KEY>}{[KEYNUM]}}
+
+ The "prvs" expansion item takes three arguments: A qualified RFC2821
+ email address, a key and an (optional) key number. All arguments are
+ expanded before being used, so it is easily possible to lookup a key
+ and key number using the address as the lookup key. The key number is
+ optional and defaults to "0". The item will expand to a "prvs"-signed
+ email address, to be typically used with the "return_path" option on
+ a smtp transport. The decision if BATV should be used with a given
+ sender/recipient pair should be done on router level, to avoid having
+ to set "max_rcpt = 1" on the transport.
+
+
+ ${prvscheck {<ADDRESS>}{<SECRET>}{<RETURN_STRING>}}
+
+ The "prvscheck" expansion item takes three arguments. Argument 1 is
+ expanded first. When the expansion does not yield a SYNTACTICALLY
+ valid "prvs"-scheme address, the whole "prvscheck" item expands to
+ the empty string. If <ADDRESS> is a "prvs"-encoded address after
+ expansion, two expansion variables are set up:
+
+ $prvscheck_address Contains the "prvs"-decoded version of
+ the address from argument 1.
+
+ $prvscheck_keynum Contains the key number extracted from
+ the "prvs"-address in argument 1.
+
+ These two variables can be used in the expansion code of argument 2
+ to retrieve the <SECRET>. The VALIDITY of the "prvs"-signed address
+ is then checked. The result is stored in yet another expansion
+ variable:
+
+ $prvscheck_result Contains the result of a "prvscheck"
+ expansion: Unset (the empty string) for
+ failure, "1" for success.
+
+ The "prvscheck" expansion expands to the empty string if <ADDRESS>
+ is not a SYNTACTICALLY valid "prvs"-scheme address. Otherwise,
+ argument 3 defines what "prvscheck" expands to: If argument 3
+ is the empty string, "prvscheck" expands to the decoded version
+ of the address (no matter if it is CRYPTOGRAPHICALLY valid or not).
+ If argument 3 expands to a non-empty string, "prvscheck" expands
+ to that string.
+
+
+ Usage example
+ -------------
+
+ Macro:
+
+ PRVSCHECK_SQL = ${lookup mysql{SELECT secret FROM batv_prvs WHERE \
+ sender='${quote_mysql:$prvscheck_address}'}{$value}}
+
+ RCPT ACL:
+
+ # Bounces: drop unsigned addresses for BATV senders
+ deny message = This address does not send an unsigned reverse path.
+ senders = :
+ recipients = +batv_recipients
+
+ # Bounces: In case of prvs-signed address, check signature.
+ deny message = Invalid reverse path signature.
+ senders = :
+ condition = ${prvscheck {$local_part@$domain}{PRVSCHECK_SQL}{1}}
+ !condition = $prvscheck_result
+
+ Top-Level Router:
+
+ batv_redirect:
+ driver = redirect
+ data = ${prvscheck {$local_part@$domain}{PRVSCHECK_SQL}{}}
+
+ Transport (referenced by router that makes decision if
+ BATV is applicable):
+
+ external_smtp_batv:
+ driver = smtp
+ return_path = ${prvs {$return_path} \
+ {${lookup mysql{SELECT \
+ secret FROM batv_prvs WHERE \
+ sender='${quote_mysql:$sender_address}'} \
+ {$value}fail}}}
+
+PH/04 There are two new options that control the retrying done by the daemon
+ at startup when it cannot immediately bind a socket (typically because
+ the socket is already in use). The default values reproduce what were
+ built-in constants previously: daemon_startup_retries defines the number
+ of retries after the first failure (default 9); daemon_startup_sleep
+ defines the length of time to wait between retries (default 30s).
+
+PH/05 There is now a new ${if condition called "match_ip". It is similar to
+ match_domain, etc. It must be followed by two argument strings. The first
+ (after expansion) must be an IP address or an empty string. The second
+ (after expansion) is a restricted host list that can match only an IP
+ address, not a host name. For example:
+
+ ${if match_ip{$sender_host_address}{1.2.3.4:5.6.7.8}{...}{...}}
+
+ The specific types of host list item that are permitted in the list are
+ shown below. Consult the manual section on host lists for further
+ details.
+
+ . An IP address, optionally with a CIDR mask.
+
+ . A single asterisk matches any IP address.
+
+ . An empty item matches only if the IP address is empty. This could be
+ useful for testing for a locally submitted message or one from specific
+ hosts in a single test such as
+
+ ${if match_ip{$sender_host_address}{:4.3.2.1:...}{...}{...}}
+
+ where the first item in the list is the empty string.
+
+ . The item @[] matches any of the local host's interface addresses.
+
+ . Lookups are assumed to be "net-" style lookups, even if "net-" is not
+ specified. Thus, the following are equivalent:
+
+ ${if match_ip{$sender_host_address}{lsearch;/some/file}...
+ ${if match_ip{$sender_host_address}{net-lsearch;/some/file}...
+
+ You do need to specify the "net-" prefix if you want to specify a
+ specific address mask, for example, by using "net24-".
+
+PH/06 The "+all" debug selector used to set the flags for all possible output;
+ it is something that people tend to use semi-automatically when
+ generating debug output for me or for the list. However, by including
+ "+memory", an awful lot of output that is very rarely of interest was
+ generated. I have changed this so that "+all" no longer includes
+ "+memory". However, "-all" still turns everything off.
+
Version 4.51
------------
projects / exim.git / blobdiff