-$Cambridge: exim/doc/doc-txt/NewStuff,v 1.48 2005/05/31 10:58:18 ph10 Exp $
+$Cambridge: exim/doc/doc-txt/NewStuff,v 1.77 2005/11/21 09:51:21 ph10 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 4.52
------------------
-
-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.
-
- 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} }
-
-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.
-
-
-Version 4.51
+Version 4.60
------------
-PH/01 The format in which GnuTLS parameters are written to the gnutls-param
- file in the spool directory has been changed. This change has been made
- to alleviate problems that some people had with the generation of the
- parameters by Exim when /dev/random was exhausted. In this situation,
- Exim would hang until /dev/random acquired some more entropy.
-
- The new code exports and imports the DH and RSA parameters in PEM
- format. This means that the parameters can be generated externally using
- the certtool command that is part of GnuTLS.
-
- To replace the parameters with new ones, instead of deleting the file
- and letting Exim re-create it, you can generate new parameters using
- certtool and, when this has been done, replace Exim's cache file by
- renaming. The relevant commands are something like this:
-
- # rm -f new.params
- # touch new.params
- # chown exim:exim new.params
- # chmod 0400 new.params
- # certtool --generate-privkey --bits 512 >new.params
- # echo "" >>new.params
- # certtool --generate-dh-params --bits 1024 >> new.params
- # mv new.params params
-
- If Exim never has to generate the parameters itself, the possibility of
- stalling is removed.
-
-PH/02 A new expansion item for dynamically loading and calling a locally-
- written C function is now provided, if Exim is compiled with
-
- EXPAND_DLFUNC=yes
-
- set in Local/Makefile. The facility is not included by default (a
- suitable error is given if you try to use it when it is not there.)
-
- If you enable EXPAND_DLFUNC, you should also be aware of the new redirect
- router option forbid_filter_dlfunc. If you have unprivileged users on
- your system who are permitted to create filter files, you might want to
- set forbid_filter_dlfunc=true in the appropriate router, to stop them
- using ${dlfunc to run code within Exim.
-
- You load and call an external function like this:
-
- ${dlfunc{/some/file}{function}{arg1}{arg2}...}
-
- Once loaded, Exim remembers the dynamically loaded object so that it
- doesn't reload the same object file in the same Exim process (but of
- course Exim does start new processes frequently).
-
- There may be from zero to eight arguments to the function. When compiling
- a local function that is to be called in this way, local_scan.h should be
- included. The Exim variables and functions that are defined by that API
- are also available for dynamically loaded functions. The function itself
- must have the following type:
-
- int dlfunction(uschar **yield, int argc, uschar *argv[])
-
- Where "uschar" is a typedef for "unsigned char" in local_scan.h. The
- function should return one of the following values:
+The documentation is up-to-date for the 4.60 release. Major new features since
+the 4.50 release are:
- OK Success. The string that is placed in "yield" is put into
- the expanded string that is being built.
+. Support for SQLite.
- FAIL A non-forced expansion failure occurs, with the error
- message taken from "yield", if it is set.
+. Support for IGNOREQUOTA in LMTP.
- FAIL_FORCED A forced expansion failure occurs, with the error message
- taken from "yield" if it is set.
+. Extensions to the "submission mode" features.
- ERROR Same as FAIL, except that a panic log entry is written.
+. Support for Client SMTP Authorization (CSA).
- When compiling a function that is to be used in this way with gcc,
- you need to add -shared to the gcc command. Also, in the Exim build-time
- configuration, you must add -export-dynamic to EXTRALIBS.
+. Support for ratelimiting hosts and users.
-TF/01 $received_time is a new expansion variable containing the time and date
- as a number of seconds since the start of the Unix epoch when the
- current message was received.
+. New expansion items to help with the BATV "prvs" scheme.
-PH/03 There is a new value for RADIUS_LIB_TYPE that can be set in
- Local/Makefile. It is RADIUSCLIENTNEW, and it requests that the new API,
- in use from radiusclient 0.4.0 onwards, be used. It does not appear to be
- possible to detect the different versions automatically.
-
-PH/04 There is a new option called acl_not_smtp_mime that allows you to scan
- MIME parts in non-SMTP messages. It operates in exactly the same way as
- acl_smtp_mime
-
-PH/05 It is now possible to redefine a macro within the configuration file.
- The macro must have been previously defined within the configuration (or
- an included file). A definition on the command line using the -D option
- causes all definitions and redefinitions within the file to be ignored.
- In other words, -D overrides any values that are set in the file.
- Redefinition is specified by using '==' instead of '='. For example:
-
- MAC1 = initial value
- ...
- MAC1 == updated value
-
- Redefinition does not alter the order in which the macros are applied to
- the subsequent lines of the configuration file. It is still the same
- order in which the macros were originally defined. All that changes is
- the macro's value. Redefinition makes it possible to accumulate values.
- For example:
-
- MAC1 = initial value
- ...
- MAC1 == MAC1 and something added
-
- This can be helpful in situations where the configuration file is built
- from a number of other files.
-
-PH/06 Macros may now be defined or redefined between router, transport,
- authenticator, or ACL definitions, as well as in the main part of the
- configuration. They may not, however, be changed within an individual
- driver or ACL, or in the local_scan, retry, or rewrite sections of the
- configuration.
-
-PH/07 $acl_verify_message is now set immediately after the failure of a
- verification in an ACL, and so is available in subsequent modifiers. In
- particular, the message can be preserved by coding like this:
-
- warn !verify = sender
- set acl_m0 = $acl_verify_message
-
- Previously, $acl_verify_message was set only while expanding "message"
- and "log_message" when a very denied access.
-
-PH/08 The redirect router has two new options, sieve_useraddress and
- sieve_subaddress. These are passed to a Sieve filter to specify the :user
- and :subaddress parts of an address. Both options are unset by default.
- However, when a Sieve filter is run, if sieve_useraddress is unset, the
- entire original local part (including any prefix or suffix) is used for
- :user. An unset subaddress is treated as an empty subaddress.
-
-PH/09 Quota values can be followed by G as well as K and M.
-
-PH/10 $message_linecount is a new variable that contains the total number of
- lines in the header and body of the message. Compare $body_linecount,
- which is the count for the body only. During the DATA and
- content-scanning ACLs, $message_linecount contains the number of lines
- received. Before delivery happens (that is, before filters, routers, and
- transports run) the count is increased to include the Received: header
- line that Exim standardly adds, and also any other header lines that are
- added by ACLs. The blank line that separates the message header from the
- body is not counted. Here is an example of the use of this variable in a
- DATA ACL:
-
- deny message = Too many lines in message header
- condition = \
- ${if <{250}{${eval: $message_linecount - $body_linecount}}}
-
- In the MAIL and RCPT ACLs, the value is zero because at that stage the
- message has not yet been received.
-
-PH/11 In a ${run expansion, the variable $value (which contains the standard
- output) is now also usable in the "else" string.
-
-PH/12 In a pipe transport, although a timeout while waiting for the pipe
- process to complete was treated as a delivery failure, a timeout while
- writing the message to the pipe was logged, but erroneously treated as a
- successful delivery. Such timeouts include transport filter timeouts. For
- consistency with the overall process timeout, these timeouts are now
- treated as errors, giving rise to delivery failures by default. However,
- there is now a new Boolean option for the pipe transport called
- timeout_defer, which, if set TRUE, converts the failures into defers for
- both kinds of timeout. A transport filter timeout is now identified in
- the log output.
-
-
-Version 4.50
-------------
+. A "match_ip" condition, that matches an IP address against a list.
-The documentation is up-to-date for the 4.50 release.
+There are many more minor changes.
****
projects / exim.git / blobdiff