doc/doc-txt/NewStuff

   1 $Cambridge: exim/doc/doc-txt/NewStuff,v 1.44 2005/05/23 15:44:06 fanf2 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 TF/02 There have been two changes concerned with submission mode:
  85
  86       Until now submission mode always left the return path alone, whereas
  87       locally-submitted messages from untrusted users have the return path
  88       fixed to the user's email address. Submission mode now fixes the return
  89       path to the same address as is used to create the Sender: header. If
  90       /sender_retain is specified then both the Sender: header and the return
  91       path are left alone.
  92
  93       Note that the changes caused by submission mode take effect after the
  94       predata ACL. This means that any sender checks performed before the
  95       fix-ups will use the untrusted sender address specified by the user, not
  96       the trusted sender address specified by submission mode. Although this
  97       might be slightly unexpected, it does mean that you can configure ACL
  98       checks to spot that a user is trying to spoof another's address, for
  99       example.
 100
 101       There is also a new /name= option for submission mode which allows you
 102       to specify the user's full name to be included in the Sender: header.
 103       For example:
 104
 105         accept authenticated = *
 106                control = submission/name=${lookup {$authenticated_id} \
 107                                            lsearch {/etc/exim/namelist} }
 108
 109       The namelist file contains entries like
 110
 111         fanf: Tony Finch
 112
 113       And the resulting Sender: header looks like
 114
 115         Sender: Tony Finch <fanf@exim.org>
 116
 117 TF/03 The control = fakereject ACL modifier now has a fakedefer counterpart,
 118       which works in exactly the same way except it causes a fake SMTP 450
 119       response after the message data instead of a fake SMTP 550 response.
 120       You must take care when using fakedefer because it will cause messages
 121       to be duplicated when the sender retries. Therefore you should not use
 122       fakedefer if the message will be delivered normally.
 123
 124
 125 Version 4.51
 126 ------------
 127
 128 PH/01 The format in which GnuTLS parameters are written to the gnutls-param
 129       file in the spool directory has been changed. This change has been made
 130       to alleviate problems that some people had with the generation of the
 131       parameters by Exim when /dev/random was exhausted. In this situation,
 132       Exim would hang until /dev/random acquired some more entropy.
 133
 134       The new code exports and imports the DH and RSA parameters in PEM
 135       format. This means that the parameters can be generated externally using
 136       the certtool command that is part of GnuTLS.
 137
 138       To replace the parameters with new ones, instead of deleting the file
 139       and letting Exim re-create it, you can generate new parameters using
 140       certtool and, when this has been done, replace Exim's cache file by
 141       renaming. The relevant commands are something like this:
 142
 143         # rm -f new.params
 144         # touch new.params
 145         # chown exim:exim new.params
 146         # chmod 0400 new.params
 147         # certtool --generate-privkey --bits 512 >new.params
 148         # echo "" >>new.params
 149         # certtool --generate-dh-params --bits 1024 >> new.params
 150         # mv new.params params
 151
 152       If Exim never has to generate the parameters itself, the possibility of
 153       stalling is removed.
 154
 155 PH/02 A new expansion item for dynamically loading and calling a locally-
 156       written C function is now provided, if Exim is compiled with
 157
 158         EXPAND_DLFUNC=yes
 159
 160       set in Local/Makefile. The facility is not included by default (a
 161       suitable error is given if you try to use it when it is not there.)
 162
 163       If you enable EXPAND_DLFUNC, you should also be aware of the new redirect
 164       router option forbid_filter_dlfunc. If you have unprivileged users on
 165       your system who are permitted to create filter files, you might want to
 166       set forbid_filter_dlfunc=true in the appropriate router, to stop them
 167       using ${dlfunc to run code within Exim.
 168
 169       You load and call an external function like this:
 170
 171         ${dlfunc{/some/file}{function}{arg1}{arg2}...}
 172
 173       Once loaded, Exim remembers the dynamically loaded object so that it
 174       doesn't reload the same object file in the same Exim process (but of
 175       course Exim does start new processes frequently).
 176
 177       There may be from zero to eight arguments to the function. When compiling
 178       a local function that is to be called in this way, local_scan.h should be
 179       included. The Exim variables and functions that are defined by that API
 180       are also available for dynamically loaded functions. The function itself
 181       must have the following type:
 182
 183         int dlfunction(uschar **yield, int argc, uschar *argv[])
 184
 185       Where "uschar" is a typedef for "unsigned char" in local_scan.h. The
 186       function should return one of the following values:
 187
 188       OK            Success. The string that is placed in "yield" is put into
 189                     the expanded string that is being built.
 190
 191       FAIL          A non-forced expansion failure occurs, with the error
 192                     message taken from "yield", if it is set.
 193
 194       FAIL_FORCED   A forced expansion failure occurs, with the error message
 195                     taken from "yield" if it is set.
 196
 197       ERROR         Same as FAIL, except that a panic log entry is written.
 198
 199       When compiling a function that is to be used in this way with gcc,
 200       you need to add -shared to the gcc command. Also, in the Exim build-time
 201       configuration, you must add -export-dynamic to EXTRALIBS.
 202
 203 TF/01 $received_time is a new expansion variable containing the time and date
 204       as a number of seconds since the start of the Unix epoch when the
 205       current message was received.
 206
 207 PH/03 There is a new value for RADIUS_LIB_TYPE that can be set in
 208       Local/Makefile. It is RADIUSCLIENTNEW, and it requests that the new API,
 209       in use from radiusclient 0.4.0 onwards, be used. It does not appear to be
 210       possible to detect the different versions automatically.
 211
 212 PH/04 There is a new option called acl_not_smtp_mime that allows you to scan
 213       MIME parts in non-SMTP messages. It operates in exactly the same way as
 214       acl_smtp_mime
 215
 216 PH/05 It is now possible to redefine a macro within the configuration file.
 217       The macro must have been previously defined within the configuration (or
 218       an included file). A definition on the command line using the -D option
 219       causes all definitions and redefinitions within the file to be ignored.
 220       In other words, -D overrides any values that are set in the file.
 221       Redefinition is specified by using '==' instead of '='. For example:
 222
 223         MAC1 =  initial value
 224         ...
 225         MAC1 == updated value
 226
 227       Redefinition does not alter the order in which the macros are applied to
 228       the subsequent lines of the configuration file. It is still the same
 229       order in which the macros were originally defined. All that changes is
 230       the macro's value. Redefinition makes it possible to accumulate values.
 231       For example:
 232
 233         MAC1 =  initial value
 234         ...
 235         MAC1 == MAC1 and something added
 236
 237       This can be helpful in situations where the configuration file is built
 238       from a number of other files.
 239
 240 PH/06 Macros may now be defined or redefined between router, transport,
 241       authenticator, or ACL definitions, as well as in the main part of the
 242       configuration. They may not, however, be changed within an individual
 243       driver or ACL, or in the local_scan, retry, or rewrite sections of the
 244       configuration.
 245
 246 PH/07 $acl_verify_message is now set immediately after the failure of a
 247       verification in an ACL, and so is available in subsequent modifiers. In
 248       particular, the message can be preserved by coding like this:
 249
 250          warn  !verify = sender
 251                set acl_m0 = $acl_verify_message
 252
 253       Previously, $acl_verify_message was set only while expanding "message"
 254       and "log_message" when a very denied access.
 255
 256 PH/08 The redirect router has two new options, sieve_useraddress and
 257       sieve_subaddress. These are passed to a Sieve filter to specify the :user
 258       and :subaddress parts of an address. Both options are unset by default.
 259       However, when a Sieve filter is run, if sieve_useraddress is unset, the
 260       entire original local part (including any prefix or suffix) is used for
 261       :user. An unset subaddress is treated as an empty subaddress.
 262
 263 PH/09 Quota values can be followed by G as well as K and M.
 264
 265 PH/10 $message_linecount is a new variable that contains the total number of
 266       lines in the header and body of the message. Compare $body_linecount,
 267       which is the count for the body only. During the DATA and
 268       content-scanning ACLs, $message_linecount contains the number of lines
 269       received. Before delivery happens (that is, before filters, routers, and
 270       transports run) the count is increased to include the Received: header
 271       line that Exim standardly adds, and also any other header lines that are
 272       added by ACLs. The blank line that separates the message header from the
 273       body is not counted. Here is an example of the use of this variable in a
 274       DATA ACL:
 275
 276         deny message   = Too many lines in message header
 277              condition = \
 278                ${if <{250}{${eval: $message_linecount - $body_linecount}}}
 279
 280       In the MAIL and RCPT ACLs, the value is zero because at that stage the
 281       message has not yet been received.
 282
 283 PH/11 In a ${run expansion, the variable $value (which contains the standard
 284       output) is now also usable in the "else" string.
 285
 286 PH/12 In a pipe transport, although a timeout while waiting for the pipe
 287       process to complete was treated as a delivery failure, a timeout while
 288       writing the message to the pipe was logged, but erroneously treated as a
 289       successful delivery. Such timeouts include transport filter timeouts. For
 290       consistency with the overall process timeout, these timeouts are now
 291       treated as errors, giving rise to delivery failures by default. However,
 292       there is now a new Boolean option for the pipe transport called
 293       timeout_defer, which, if set TRUE, converts the failures into defers for
 294       both kinds of timeout. A transport filter timeout is now identified in
 295       the log output.
 296
 297
 298 Version 4.50
 299 ------------
 300
 301 The documentation is up-to-date for the 4.50 release.
 302
 303 ****