doc/doc-txt/NewStuff

   1 $Cambridge: exim/doc/doc-txt/NewStuff,v 1.42 2005/05/17 15:00:04 ph10 Exp $
   2
   3 New Features in Exim
   4 --------------------
   5
   6 This file contains descriptions of new features that have been added to Exim,
   7 but have not yet made it into the main manual (which is most conveniently
   8 updated when there is a relatively large batch of changes). The doc/ChangeLog
   9 file contains a listing of all changes, including bug fixes.
  10
  11
  12 Exim version 4.52
  13 -----------------
  14
  15 TF/01 Support for checking Client SMTP Authorization has been added. CSA is a
  16       system which allows a site to advertise which machines are and are not
  17       permitted to send email. This is done by placing special SRV records in
  18       the DNS, which are looked up using the client's HELO domain. At this
  19       time CSA is still an Internet-Draft.
  20
  21       Client SMTP Authorization checks are performed by the ACL condition
  22       verify=csa. This will fail if the client is not authorized. If there is
  23       a DNS problem, or if no valid CSA SRV record is found, or if the client
  24       is authorized, the condition succeeds. These three cases can be
  25       distinguished using the expansion variable $csa_status, which can take
  26       one of the values "fail", "defer", "unknown", or "ok". The condition
  27       does not itself defer because that would be likely to cause problems
  28       for legitimate email.
  29
  30       The error messages produced by the CSA code include slightly more
  31       detail. If $csa_status is "defer" this may be because of problems
  32       looking up the CSA SRV record, or problems looking up the CSA target
  33       address record. There are four reasons for $csa_status being "fail":
  34       the client's host name is explicitly not authorized; the client's IP
  35       address does not match any of the CSA target IP addresses; the client's
  36       host name is authorized but it has no valid target IP addresses (e.g.
  37       the target's addresses are IPv6 and the client is using IPv4); or the
  38       client's host name has no CSA SRV record but a parent domain has
  39       asserted that all subdomains must be explicitly authorized.
  40
  41       The verify=csa condition can take an argument which is the domain to
  42       use for the DNS query. The default is verify=csa/$sender_helo_name.
  43
  44       This implementation includes an extension to CSA. If the query domain
  45       is an address literal such as [192.0.2.95], or if it is a bare IP
  46       address, Exim will search for CSA SRV records in the reverse DNS as if
  47       the HELO domain was e.g. 95.2.0.192.in-addr.arpa. Therefore it is
  48       meaningful to say, for example, verify=csa/$sender_host_address - in
  49       fact, this is the check that Exim performs if the client does not say
  50       HELO. This extension can be turned off by setting the main
  51       configuration option dns_csa_use_reverse = false.
  52
  53       If a CSA SRV record is not found for the domain itself, then a search
  54       is performed through its parent domains for a record which might be
  55       making assertions about subdomains. The maximum depth of this search is
  56       limited using the main configuration option dns_csa_search_limit, which
  57       takes the value 5 by default. Exim does not look for CSA SRV records in
  58       a top level domain, so the default settings handle HELO domains as long
  59       as seven (hostname.five.four.three.two.one.com) which encompasses the
  60       vast majority of legitimate HELO domains.
  61
  62       The dnsdb lookup also has support for CSA. Although dnsdb already
  63       supports SRV lookups, this is not sufficient because of the extra
  64       parent domain search behaviour of CSA, and (as with PTR lookups)
  65       dnsdb also turns IP addresses into lookups in the reverse DNS space.
  66       The result of ${lookup dnsdb {csa=$sender_helo_name} } has two
  67       space-separated fields: an authorization code and a target host name.
  68       The authorization code can be "Y" for yes, "N" for no, "X" for explicit
  69       authorization required but absent, or "?" for unknown.
  70
  71 PH/01 The amount of output produced by the "make" process has been reduced,
  72       because the compile lines are often rather long, making it all pretty
  73       unreadable. The new style is along the lines of the 2.6 Linux kernel:
  74       just a short line for each module that is being compiled or linked.
  75       However, it is still possible to get the full output, by calling "make"
  76       like this:
  77
  78         FULLECHO='' make -e
  79
  80       The value of FULLECHO defaults to "@", the flag character that suppresses
  81       command reflection in "make". When you ask for the full output, it is
  82       given in addition to the the short output.
  83
  84 PH/02 There have been two changes concerned with submission mode:
  85
  86       (a) A new option, /name=value, makes it possible to supply a user name
  87           to be inserted into any created Sender: header line. Typically, this
  88           would be looked up from $authenticated_id.
  89
  90       (b) The envelope sender address is forced to be the same as the
  91           submission mode sender address.
  92
  93
  94 Version 4.51
  95 ------------
  96
  97 PH/01 The format in which GnuTLS parameters are written to the gnutls-param
  98       file in the spool directory has been changed. This change has been made
  99       to alleviate problems that some people had with the generation of the
 100       parameters by Exim when /dev/random was exhausted. In this situation,
 101       Exim would hang until /dev/random acquired some more entropy.
 102
 103       The new code exports and imports the DH and RSA parameters in PEM
 104       format. This means that the parameters can be generated externally using
 105       the certtool command that is part of GnuTLS.
 106
 107       To replace the parameters with new ones, instead of deleting the file
 108       and letting Exim re-create it, you can generate new parameters using
 109       certtool and, when this has been done, replace Exim's cache file by
 110       renaming. The relevant commands are something like this:
 111
 112         # rm -f new.params
 113         # touch new.params
 114         # chown exim:exim new.params
 115         # chmod 0400 new.params
 116         # certtool --generate-privkey --bits 512 >new.params
 117         # echo "" >>new.params
 118         # certtool --generate-dh-params --bits 1024 >> new.params
 119         # mv new.params params
 120
 121       If Exim never has to generate the parameters itself, the possibility of
 122       stalling is removed.
 123
 124 PH/02 A new expansion item for dynamically loading and calling a locally-
 125       written C function is now provided, if Exim is compiled with
 126
 127         EXPAND_DLFUNC=yes
 128
 129       set in Local/Makefile. The facility is not included by default (a
 130       suitable error is given if you try to use it when it is not there.)
 131
 132       If you enable EXPAND_DLFUNC, you should also be aware of the new redirect
 133       router option forbid_filter_dlfunc. If you have unprivileged users on
 134       your system who are permitted to create filter files, you might want to
 135       set forbid_filter_dlfunc=true in the appropriate router, to stop them
 136       using ${dlfunc to run code within Exim.
 137
 138       You load and call an external function like this:
 139
 140         ${dlfunc{/some/file}{function}{arg1}{arg2}...}
 141
 142       Once loaded, Exim remembers the dynamically loaded object so that it
 143       doesn't reload the same object file in the same Exim process (but of
 144       course Exim does start new processes frequently).
 145
 146       There may be from zero to eight arguments to the function. When compiling
 147       a local function that is to be called in this way, local_scan.h should be
 148       included. The Exim variables and functions that are defined by that API
 149       are also available for dynamically loaded functions. The function itself
 150       must have the following type:
 151
 152         int dlfunction(uschar **yield, int argc, uschar *argv[])
 153
 154       Where "uschar" is a typedef for "unsigned char" in local_scan.h. The
 155       function should return one of the following values:
 156
 157       OK            Success. The string that is placed in "yield" is put into
 158                     the expanded string that is being built.
 159
 160       FAIL          A non-forced expansion failure occurs, with the error
 161                     message taken from "yield", if it is set.
 162
 163       FAIL_FORCED   A forced expansion failure occurs, with the error message
 164                     taken from "yield" if it is set.
 165
 166       ERROR         Same as FAIL, except that a panic log entry is written.
 167
 168       When compiling a function that is to be used in this way with gcc,
 169       you need to add -shared to the gcc command. Also, in the Exim build-time
 170       configuration, you must add -export-dynamic to EXTRALIBS.
 171
 172 TF/01 $received_time is a new expansion variable containing the time and date
 173       as a number of seconds since the start of the Unix epoch when the
 174       current message was received.
 175
 176 PH/03 There is a new value for RADIUS_LIB_TYPE that can be set in
 177       Local/Makefile. It is RADIUSCLIENTNEW, and it requests that the new API,
 178       in use from radiusclient 0.4.0 onwards, be used. It does not appear to be
 179       possible to detect the different versions automatically.
 180
 181 PH/04 There is a new option called acl_not_smtp_mime that allows you to scan
 182       MIME parts in non-SMTP messages. It operates in exactly the same way as
 183       acl_smtp_mime
 184
 185 PH/05 It is now possible to redefine a macro within the configuration file.
 186       The macro must have been previously defined within the configuration (or
 187       an included file). A definition on the command line using the -D option
 188       causes all definitions and redefinitions within the file to be ignored.
 189       In other words, -D overrides any values that are set in the file.
 190       Redefinition is specified by using '==' instead of '='. For example:
 191
 192         MAC1 =  initial value
 193         ...
 194         MAC1 == updated value
 195
 196       Redefinition does not alter the order in which the macros are applied to
 197       the subsequent lines of the configuration file. It is still the same
 198       order in which the macros were originally defined. All that changes is
 199       the macro's value. Redefinition makes it possible to accumulate values.
 200       For example:
 201
 202         MAC1 =  initial value
 203         ...
 204         MAC1 == MAC1 and something added
 205
 206       This can be helpful in situations where the configuration file is built
 207       from a number of other files.
 208
 209 PH/06 Macros may now be defined or redefined between router, transport,
 210       authenticator, or ACL definitions, as well as in the main part of the
 211       configuration. They may not, however, be changed within an individual
 212       driver or ACL, or in the local_scan, retry, or rewrite sections of the
 213       configuration.
 214
 215 PH/07 $acl_verify_message is now set immediately after the failure of a
 216       verification in an ACL, and so is available in subsequent modifiers. In
 217       particular, the message can be preserved by coding like this:
 218
 219          warn  !verify = sender
 220                set acl_m0 = $acl_verify_message
 221
 222       Previously, $acl_verify_message was set only while expanding "message"
 223       and "log_message" when a very denied access.
 224
 225 PH/08 The redirect router has two new options, sieve_useraddress and
 226       sieve_subaddress. These are passed to a Sieve filter to specify the :user
 227       and :subaddress parts of an address. Both options are unset by default.
 228       However, when a Sieve filter is run, if sieve_useraddress is unset, the
 229       entire original local part (including any prefix or suffix) is used for
 230       :user. An unset subaddress is treated as an empty subaddress.
 231
 232 PH/09 Quota values can be followed by G as well as K and M.
 233
 234 PH/10 $message_linecount is a new variable that contains the total number of
 235       lines in the header and body of the message. Compare $body_linecount,
 236       which is the count for the body only. During the DATA and
 237       content-scanning ACLs, $message_linecount contains the number of lines
 238       received. Before delivery happens (that is, before filters, routers, and
 239       transports run) the count is increased to include the Received: header
 240       line that Exim standardly adds, and also any other header lines that are
 241       added by ACLs. The blank line that separates the message header from the
 242       body is not counted. Here is an example of the use of this variable in a
 243       DATA ACL:
 244
 245         deny message   = Too many lines in message header
 246              condition = \
 247                ${if <{250}{${eval: $message_linecount - $body_linecount}}}
 248
 249       In the MAIL and RCPT ACLs, the value is zero because at that stage the
 250       message has not yet been received.
 251
 252 PH/11 In a ${run expansion, the variable $value (which contains the standard
 253       output) is now also usable in the "else" string.
 254
 255 PH/12 In a pipe transport, although a timeout while waiting for the pipe
 256       process to complete was treated as a delivery failure, a timeout while
 257       writing the message to the pipe was logged, but erroneously treated as a
 258       successful delivery. Such timeouts include transport filter timeouts. For
 259       consistency with the overall process timeout, these timeouts are now
 260       treated as errors, giving rise to delivery failures by default. However,
 261       there is now a new Boolean option for the pipe transport called
 262       timeout_defer, which, if set TRUE, converts the failures into defers for
 263       both kinds of timeout. A transport filter timeout is now identified in
 264       the log output.
 265
 266
 267 Version 4.50
 268 ------------
 269
 270 The documentation is up-to-date for the 4.50 release.
 271
 272 ****