-$Cambridge: exim/doc/doc-txt/NewStuff,v 1.127 2007/01/17 11:17:58 ph10 Exp $
+$Cambridge: exim/doc/doc-txt/NewStuff,v 1.144 2007/03/13 11:06:48 ph10 Exp $
New Features in Exim
--------------------
When the DNS lookup yields only a single IP address, there is no difference
between = and == and between & and =&.
+ 3. Up till now, the only control over which cipher suites GnuTLS uses has been
+ for the cipher algorithms. New options have been added to allow some of the
+ other parameters to be varied. Here is complete documentation for the
+ available features:
+
+ GnuTLS allows the caller to specify separate lists of permitted key
+ exchange methods, main cipher algorithms, and MAC algorithms. These may be
+ used in any combination to form a specific cipher suite. This is unlike
+ OpenSSL, where complete cipher names can be passed to its control function.
+ GnuTLS also allows a list of acceptable protocols to be supplied.
+
+ For compatibility with OpenSSL, the tls_require_ciphers option can be set
+ to complete cipher suite names such as RSA_ARCFOUR_SHA, but for GnuTLS this
+ option controls only the cipher algorithms. Exim searches each item in the
+ list for the name of an available algorithm. For example, if the list
+ contains RSA_AES_SHA, then AES is recognized, and the behaviour is exactly
+ the same as if just AES were given.
+
+ There are additional options called gnutls_require_kx, gnutls_require_mac,
+ and gnutls_require_protocols that can be used to restrict the key exchange
+ methods, MAC algorithms, and protocols, respectively. These options are
+ ignored if OpenSSL is in use.
+
+ All four options are available as global options, controlling how Exim
+ behaves as a server, and also as options of the smtp transport, controlling
+ how Exim behaves as a client. All the values are string expanded. After
+ expansion, the values must be colon-separated lists, though the separator
+ can be changed in the usual way.
+
+ Each of the four lists starts out with a default set of algorithms. If the
+ first item in one of the "require" options does _not_ start with an
+ exclamation mark, all the default items are deleted. In this case, only
+ those that are explicitly specified can be used. If the first item in one
+ of the "require" items _does_ start with an exclamation mark, the defaults
+ are left on the list.
+
+ Then, any item that starts with an exclamation mark causes the relevant
+ entry to be removed from the list, and any item that does not start with an
+ exclamation mark causes a new entry to be added to the list. Unrecognized
+ items in the list are ignored. Thus:
+
+ tls_require_ciphers = !ARCFOUR
+
+ allows all the defaults except ARCFOUR, whereas
+
+ tls_require_ciphers = AES : 3DES
+
+ allows only cipher suites that use AES or 3DES. For tls_require_ciphers
+ the recognized names are AES_256, AES_128, AES (both of the preceding),
+ 3DES, ARCFOUR_128, ARCFOUR_40, and ARCFOUR (both of the preceding). The
+ default list does not contain all of these; it just has AES_256, AES_128,
+ 3DES, and ARCFOUR_128.
+
+ For gnutls_require_kx, the recognized names are DHE_RSA, RSA (which
+ includes DHE_RSA), DHE_DSS, and DHE (which includes both DHE_RSA and
+ DHE_DSS). The default list contains RSA, DHE_DSS, DHE_RSA.
+
+ For gnutls_require_mac, the recognized names are SHA (synonym SHA1), and
+ MD5. The default list contains SHA, MD5.
+
+ For gnutls_require_protocols, the recognized names are TLS1 and SSL3.
+ The default list contains TLS1, SSL3.
+
+ In a server, the order of items in these lists is unimportant. The server
+ will advertise the availability of all the relevant cipher suites. However,
+ in a client, the order in the tls_require_ciphers list specifies a
+ preference order for the cipher algorithms. The first one in the client's
+ list that is also advertised by the server is tried first.
+
+ 4. There is a new compile-time option called ENABLE_DISABLE_FSYNC. You must
+ not set this option unless you really, really, really understand what you
+ are doing. No pre-compiled distributions of Exim should ever set this
+ option. When it is set, Exim compiles a runtime option called
+ disable_fsync. If this is set true, Exim no longer calls fsync() to force
+ updated files' data to be written to disc. Unexpected events such as
+ crashes and power outages may cause data to be lost or scrambled. Beware.
+
+ When ENABLE_DISABLE_FSYNC is not set, a reference to disable_fsync in a
+ runtime configuration generates an "unknown option" error.
+
+ 5. There is a new variable called $smtp_count_at_connection_start. The name
+ is deliberately long, in order to emphasize what the contents are. This
+ variable is set greater than zero only in processes spawned by the Exim
+ daemon for handling incoming SMTP connections. When the daemon accepts a
+ new connection, it increments this variable. A copy of the variable is
+ passed to the child process that handles the connection, but its value is
+ fixed, and never changes. It is only an approximation of how many incoming
+ connections there actually are, because many other connections may come and
+ go while a single connection is being processed. When a child process
+ terminates, the daemon decrements the variable.
+
+ 6. There's a new control called no_pipelining, which does what its name
+ suggests. It turns off the advertising of the PIPELINING extension to SMTP.
+ To be useful, this control must be obeyed before Exim sends its response to
+ an EHLO command. Therefore, it should normally appear in an ACL controlled
+ by acl_smtp_connect or acl_smtp_helo.
+
+ 7. There are two new variables called $sending_ip_address and $sending_port.
+ These are set whenever an SMTP connection to another host has been set up,
+ and they contain the IP address and port of the local interface that is
+ being used. They are of interest only on hosts that have more than on IP
+ address that want to take on different personalities depending on which one
+ is being used.
+
+ 8. The expansion of the helo_data option in the smtp transport now happens
+ after the connection to the server has been made. This means that it can
+ use the value of $sending_ip_address (see 7 above) to vary the text of the
+ message. For example, if you want the string that is used for helo_data to
+ be obtained by a DNS lookup of the interface address, you could use this:
+
+ helo_data = ${lookup dnsdb{ptr=$sending_ip_address}{$value}\
+ {$primary_hostname}}
+
+ The use of helo_data applies both to sending messages and when doing
+ callouts.
+
+ 9. There is a new expansion operator ${rfc2047d: that decodes strings that
+ are encoded as per RFC 2047. Binary zero bytes are replaced by question
+ marks. Characters are converted into the character set defined by
+ headers_charset. Overlong RFC 2047 "words" are not recognized unless
+ check_rfc2047_length is set false.
+
+10. There is a new log selector called "pid", which causes the current process
+ id to be added to every log line, in square brackets, immediately after the
+ time and date.
+
+11. Exim has been modified so that it flushes SMTP output before implementing
+ a delay in an ACL. It also flushes the output before performing a callout,
+ as this can take a substantial time. These behaviours can be disabled by
+ obeying control = no_delay_flush or control = no_callout_flush,
+ respectively, at some earlier stage of the connection. The effect of the
+ new default behaviour is to disable the PIPELINING optimization in these
+ situations, in order to avoid unexpected timeouts in clients.
+
+12. There are two new expansion conditions that iterate over a list. They are
+ called forany and forall, and they are used like this:
+
+ ${if forany{<a list>}{<a condition>}{<yes-string>}{<no-string>}}
+ ${if forall{<a list>}{<a condition>}{<yes-string>}{<no-string>}}
+
+ The first argument is expanded, and the result is treated as a list. By
+ default, the list separator is a colon, but it can be changed by the normal
+ method. The second argument is interpreted as a condition that is to be
+ applied to each item in the list in turn. During the interpretation of the
+ condition, the current list item is placed in a variable called $item.
+
+ - For forany, interpretation stops if the condition is true for any item,
+ and the yes-string is then expanded. If the condition is false for all
+ items in the list, the no-string is expanded.
+
+ - For forall, interpration stops if the condition is false for any item,
+ and the no-string is then expanded. If the condition is true for all
+ items in the list, the yes-string is expanded.
+
+ Note that negation of forany means that the condition must be false for all
+ items for the overall condition to succeed, and negation of forall means
+ that the condition must be false for at least one item.
+
+ In this example, the list separator is changed to a comma:
+
+ ${if forany{<, $recipients}{match{$item}{^user3@}}{yes}{no}}
+
+ Outside a forany/forall condition, the value of $item is an empty string.
+ Its value is saved and restored while forany/forall is being processed, to
+ enable these expansion items to be nested.
+
+13. There's a new global option called dsn_from that can be used to vary the
+ contents of From: lines in bounces and other automatically generated
+ messages ("delivery status notifications" - hence the name of the option).
+ The default setting is:
+
+ dsn_from = Mail Delivery System <Mailer-Daemon@$qualify_domain>
+
+ The value is expanded every time it is needed. If the expansion fails, a
+ panic is logged, and the default setting is used.
+
+14. The smtp transport has a new option called hosts_avoid_pipelining. It can
+ be used to suppress the use of PIPELINING to certain hosts, while still
+ supporting the other SMTP extensions (cf hosts_avoid_tls).
+
+15. By default, exigrep does case-insensitive matches. There is now a -I option
+ that makes it case-sensitive. This may give a performance improvement when
+ searching large log files. Without -I, the Perl pattern matches use the /i
+ option; with -I they don't. In both cases it is possible to change the case
+ sensitivity within the pattern using (?i) or (?-i).
+
+16. A number of new features have been added to string expansions to make it
+ easier to process lists of items, typically addresses. These are as
+ follows:
+
+ * ${addresses:<string>}
+
+ The string (after expansion) is interpreted as a list of addresses in RFC
+ 2822 format, such as can be found in a To: or Cc: header line. The
+ operative address (local-part@domain) is extracted from each item, and the
+ result of the expansion is a colon-separated list, with appropriate
+ doubling of colons should any happen to be present in the email addresses.
+ Syntactically invalid RFC2822 address items are omitted from the output.
+
+ It is possible to specify a character other than colon for the output
+ separator by starting the string with > followed by the new separator
+ character. For example:
+
+ ${addresses:>& The Boss <ceo@up.stairs>, sec@base.ment (dogsbody)}
+
+ expands to "ceo@up.stairs&sec@base.ment". Compare ${address (singular),
+ which extracts the working address from a single RFC2822 address.
+
+ * ${map{<string1>}{<string2>}}
+
+ After expansion, <string1> is interpreted as a list, colon-separated by
+ default, but the separator can be changed in the usual way. For each item
+ in this list, its value is place in $item, and then <string2> is expanded
+ and added to the output as an item in a new list. The separator used for
+ the output list is the same as the one used for the input, but is not
+ included in the output. For example:
+
+ ${map{a:b:c}{[$item]}} ${map{<- x-y-z}{($item)}}
+
+ expands to "[a]:[b]:[c] (x)-(y)-(z)". At the end of the expansion, the
+ value of $item is restored to what it was before.
+
+ * ${filter{<string1>}{<condition>}}
+
+ After expansion, <string1> is interpreted as a list, colon-separated by
+ default, but the separator can be changed in the usual way. For each item
+ in this list, its value is place in $item, and then the condition is
+ evaluated. If the condition is true, $item is added to the output as an
+ item in a new list; if the condition is false, the item is discarded. The
+ separator used for the output list is the same as the one used for the
+ input, but is not included in the output. For example:
+
+ ${filter{a:b:c}{!eq{$item}{b}}
+
+ yields "a:c". At the end of the expansion, the value of $item is restored
+ to what it was before.
+
+ * ${reduce{<string1>}{<string2>}{<string3>}}
+
+ The ${reduce expansion operation reduces a list to a single, scalar string.
+ After expansion, <string1> is interpreted as a list, colon-separated by
+ default, but the separator can be changed in the usual way. Then <string2>
+ is expanded and assigned to the $value variable. After this, each item in
+ the <string1> list is assigned to $item in turn, and <string3> is expanded
+ for each of them. The result of that expansion is assigned to $value before
+ the next iteration. When the end of the list is reached, the final value of
+ $value is added to the expansion string. The ${reduce expansion item can be
+ used in a number of ways. For example, to add up a list of numbers:
+
+ ${reduce {<, 1,2,3}{0}{${eval:$value+$item}}}
+
+ The result of that expansion would be "6". The maximum of a list of numbers
+ can be found:
+
+ ${reduce {3:0:9:4:6}{0}{${if >{$item}{$value}{$item}{$value}}}}
+
+ At the end of a ${reduce expansion, the values of $item and $value is
+ restored to what they were before.
+
+17. There's a new ACL modifier called "continue". It does nothing of itself,
+ and processing of the ACL always continues with the next condition or
+ modifier. It is provided so that the side effects of expanding its argument
+ can be used. Typically this would be for updating a database. It is really
+ just a syntactic tidiness, because the following two lines have the same
+ effect:
+
+ continue = <some expansion>
+ condition = ${if eq{0}{<some expansion>}{true}{true}}
+
+18. It is now possible to use newline and other control characters (those with
+ values less than 32, plus DEL) as separators in lists. Such separators must
+ be provided literally at the time the list is processed, but the string
+ expansion that happens first means that you can write them using normal
+ escape sequences. For example, if a new-line separated list of domains is
+ generated by a lookup, you can now process it directly by a line such as
+ this:
+
+ domains = <\n ${lookup mysql{.....}}
+
+ This avoids having to change the list separator in such data. Unlike
+ printing character separators, which can be included in list items by
+ doubling, it is not possible to include a control character as data when it
+ is set as the separator. Two such characters in succession are interpreted
+ as enclosing an empty list item.
+
+19. The exigrep utility now has a -v option, which inverts the matching
+ condition.
+
Version 4.66
------------
git://git.exim.org / users / jgh / exim.git / blobdiff