Debug: more detail in dkim processing

[users/heiko/exim.git] / doc / doc-docbook / spec.xfpt

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index 7ad6f0275dde96911b6be03512e56aba6e973ef1..2c783d700ed5982bf8541a0f22d9af78517594b1 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -3162,6 +3162,10 @@ If invoked by an admin user, then &%macro%&, &%macro_list%& and &%macros%&
 are available, similarly to the drivers.  Because macros are sometimes used
 for storing passwords, this option is restricted.
 The output format is one item per line.
 are available, similarly to the drivers.  Because macros are sometimes used
 for storing passwords, this option is restricted.
 The output format is one item per line.

+.new
+For the "-bP macro <name>" form, if no such macro is found
+the exit status will be nonzero.
+.wen

 
 .vitem &%-bp%&
 .oindex "&%-bp%&"
 
 .vitem &%-bp%&
 .oindex "&%-bp%&"


@@ -5579,19 +5583,27 @@ Another two commented-out option settings follow:
 .cindex "port" "465 and 587"
 .cindex "port" "for message submission"
 .cindex "message" "submission, ports for"
 .cindex "port" "465 and 587"
 .cindex "port" "for message submission"
 .cindex "message" "submission, ports for"

-.cindex "ssmtp protocol"
+.cindex "submissions protocol"

 .cindex "smtps protocol"
 .cindex "smtps protocol"

+.cindex "ssmtp protocol"
+.cindex "SMTP" "submissions protocol"

 .cindex "SMTP" "ssmtp protocol"
 .cindex "SMTP" "smtps protocol"
 These options provide better support for roaming users who wish to use this
 server for message submission. They are not much use unless you have turned on
 TLS (as described in the previous paragraph) and authentication (about which
 .cindex "SMTP" "ssmtp protocol"
 .cindex "SMTP" "smtps protocol"
 These options provide better support for roaming users who wish to use this
 server for message submission. They are not much use unless you have turned on
 TLS (as described in the previous paragraph) and authentication (about which

-more in section &<<SECTdefconfauth>>&). The usual SMTP port 25 is often blocked
-on end-user networks, so RFC 4409 specifies that message submission should use
-port 587 instead. However some software (notably Microsoft Outlook) cannot be
-configured to use port 587 correctly, so these settings also enable the
-non-standard &"smtps"& (aka &"ssmtp"&) port 465 (see section
-&<<SECTsupobssmt>>&).
+more in section &<<SECTdefconfauth>>&).
+Mail submission from mail clients (MUAs) should be separate from inbound mail
+to your domain (MX delivery) for various good reasons (eg, ability to impose
+much saner TLS protocol and ciphersuite requirements without unintended
+consequences).
+RFC 6409 (previously 4409) specifies use of port 587 for SMTP Submission,
+which uses STARTTLS, so this is the &"submission"& port.
+RFC 8314 specifies use of port 465 as the &"submissions"& protocol,
+which should be used in preference to 587.
+You should also consider deploying SRV records to help clients find
+these ports.
+Older names for &"submissions"& are &"smtps"& and &"ssmtp"&.

 
 Two more commented-out options settings follow:
 .code
 
 Two more commented-out options settings follow:
 .code


@@ -9337,7 +9349,7 @@ 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 a separator setting is not included in the output. For example:
 .code
 separator used for the output list is the same as the one used for the
 input, but a separator setting is not included in the output. For example:
 .code

-${filter{a:b:c}{!eq{$item}{b}}
+${filter{a:b:c}{!eq{$item}{b}}}

 .endd
 yields &`a:c`&. At the end of the expansion, the value of &$item$& is restored
 to what it was before. See also the &*map*& and &*reduce*& expansion items.
 .endd
 yields &`a:c`&. At the end of the expansion, the value of &$item$& is restored
 to what it was before. See also the &*map*& and &*reduce*& expansion items.


@@ -10637,7 +10649,11 @@ the output length.  Values of 224, 256, 384 and 512 are accepted;
 with 256 being the default.
 
 The &%sha3%& expansion item is only supported if Exim has been
 with 256 being the default.
 
 The &%sha3%& expansion item is only supported if Exim has been

-compiled with GnuTLS 3.5.0 or later.
+compiled with GnuTLS 3.5.0 or later,
+.new
+or OpenSSL 1.1.1 or later.
+The macro "_CRYPTO_HASH_SHA3" will be defined if it is supported.
+.wen

 
 
 .vitem &*${stat:*&<&'string'&>&*}*&
 
 
 .vitem &*${stat:*&<&'string'&>&*}*&


@@ -11659,7 +11675,7 @@ contain the trailing slash. If &$config_file$& does not contain a slash,
 .vindex "&$config_file$&"
 The name of the main configuration file Exim is using.
 
 .vindex "&$config_file$&"
 The name of the main configuration file Exim is using.
 

-.vitem &$dkim_verify_status$& &&&
+.vitem &$dkim_verify_status$&

 Results of DKIM verification.
 For details see section &<<SECDKIMVFY>>&.
 
 Results of DKIM verification.
 For details see section &<<SECDKIMVFY>>&.
 


@@ -13408,23 +13424,32 @@ value of &%daemon_smtp_ports%& is no longer relevant in this example.)
 
 
 
 
 
 

-.section "Support for the obsolete SSMTP (or SMTPS) protocol" "SECTsupobssmt"
+.section "Support for the submissions (aka SSMTP or SMTPS) protocol" "SECTsupobssmt"
+.cindex "submissions protocol"

 .cindex "ssmtp protocol"
 .cindex "smtps protocol"
 .cindex "SMTP" "ssmtp protocol"
 .cindex "SMTP" "smtps protocol"
 .cindex "ssmtp protocol"
 .cindex "smtps protocol"
 .cindex "SMTP" "ssmtp protocol"
 .cindex "SMTP" "smtps protocol"

-Exim supports the obsolete SSMTP protocol (also known as SMTPS) that was used
-before the STARTTLS command was standardized for SMTP. Some legacy clients
-still use this protocol. If the &%tls_on_connect_ports%& option is set to a
-list of port numbers or service names,
-connections to those ports must use SSMTP. The most
-common use of this option is expected to be
+Exim supports the use of TLS-on-connect, used by mail clients in the
+&"submissions"& protocol, historically also known as SMTPS or SSMTP.
+For some years, IETF Standards Track documents only blessed the
+STARTTLS-based Submission service (port 587) while common practice was to support
+the same feature set on port 465, but using TLS-on-connect.
+If your installation needs to provide service to mail clients
+(Mail User Agents, MUAs) then you should provide service on both the 587 and
+the 465 TCP ports.
+
+If the &%tls_on_connect_ports%& option is set to a list of port numbers or
+service names, connections to those ports must first establish TLS, before
+proceeding to the application layer use of the SMTP protocol.
+
+The common use of this option is expected to be

 .code
 tls_on_connect_ports = 465
 .endd
 .code
 tls_on_connect_ports = 465
 .endd

-because 465 is the usual port number used by the legacy clients. There is also
-a command line option &%-tls-on-connect%&, which forces all ports to behave in
-this way when a daemon is started.
+per RFC 8314.
+There is also a command line option &%-tls-on-connect%&, which forces all ports
+to behave in this way when a daemon is started.

 
 &*Warning*&: Setting &%tls_on_connect_ports%& does not of itself cause the
 daemon to listen on those ports. You must still specify them in
 
 &*Warning*&: Setting &%tls_on_connect_ports%& does not of itself cause the
 daemon to listen on those ports. You must still specify them in


@@ -16899,8 +16924,8 @@ and any external programs which are passed a reference to a message data file
 will need to be aware of the potential different format.
 
 Using any of the ACL conditions noted will negate the reception benefit
 will need to be aware of the potential different format.
 
 Using any of the ACL conditions noted will negate the reception benefit

-(as a Unix-mbox-format file is contructed for them).
-The transimssion benefit is maintained.
+(as a Unix-mbox-format file is constructed for them).
+The transmission benefit is maintained.

 
 .option sqlite_lock_timeout main time 5s
 .cindex "sqlite lookup type" "lock timeout"
 
 .option sqlite_lock_timeout main time 5s
 .cindex "sqlite lookup type" "lock timeout"


@@ -17127,7 +17152,7 @@ option in the relevant &(smtp)& transport.
 separator in the usual way to avoid confusion under IPv6.
 
 &*Note*&: Under current versions of OpenSSL, when a list of more than one
 separator in the usual way to avoid confusion under IPv6.
 
 &*Note*&: Under current versions of OpenSSL, when a list of more than one

-file is used, the &$tls_in_ourcert$& veriable is unreliable.
+file is used, the &$tls_in_ourcert$& variable is unreliable.

 
 &*Note*&: OCSP stapling is not usable under OpenSSL
 when a list of more than one file is used.
 
 &*Note*&: OCSP stapling is not usable under OpenSSL
 when a list of more than one file is used.


@@ -24222,7 +24247,7 @@ as the initiator must present a cookie in the SYN segment.
 On (at least some) current Linux distributions the facility must be enabled
 in the kernel by the sysadmin before the support is usable.
 There is no option for control of the server side; if the system supports
 On (at least some) current Linux distributions the facility must be enabled
 in the kernel by the sysadmin before the support is usable.
 There is no option for control of the server side; if the system supports

-it it is always enebled.  Note that legthy operations in the connect ACL,
+it it is always enabled.  Note that lengthy operations in the connect ACL,

 such as DNSBL lookups, will still delay the emission of the SMTP banner.
 
 .option hosts_try_prdr smtp "host list&!!" *
 such as DNSBL lookups, will still delay the emission of the SMTP banner.
 
 .option hosts_try_prdr smtp "host list&!!" *


@@ -27084,22 +27109,36 @@ in order to get TLS to work.
 
 
 
 
 
 

-.section "Support for the legacy &""ssmtp""& (aka &""smtps""&) protocol" &&&
+.section "Support for the &""submissions""& (aka &""ssmtp""& and &""smtps""&) protocol" &&&

          "SECID284"
          "SECID284"

+.cindex "submissions protocol"

 .cindex "ssmtp protocol"
 .cindex "smtps protocol"
 .cindex "ssmtp protocol"
 .cindex "smtps protocol"

+.cindex "SMTP" "submissions protocol"

 .cindex "SMTP" "ssmtp protocol"
 .cindex "SMTP" "smtps protocol"
 .cindex "SMTP" "ssmtp protocol"
 .cindex "SMTP" "smtps protocol"

-Early implementations of encrypted SMTP used a different TCP port from normal
-SMTP, and expected an encryption negotiation to start immediately, instead of
-waiting for a STARTTLS command from the client using the standard SMTP
-port. The protocol was called &"ssmtp"& or &"smtps"&, and port 465 was
-allocated for this purpose.
-
-This approach was abandoned when encrypted SMTP was standardized, but there are
-still some legacy clients that use it. Exim supports these clients by means of
-the &%tls_on_connect_ports%& global option. Its value must be a list of port
-numbers; the most common use is expected to be:
+The history of port numbers for TLS in SMTP is a little messy and has been
+contentious.  As of RFC 8314, the common practice of using the historically
+allocated port 465 for "email submission but with TLS immediately upon connect
+instead of using STARTTLS" is officially blessed by the IETF, and recommended
+in preference to STARTTLS.
+
+The name originally assigned to the port was &"ssmtp"& or &"smtps"&, but as
+clarity emerged over the dual roles of SMTP, for MX delivery and Email
+Submission, nomenclature has shifted.  The modern name is now &"submissions"&.
+
+This approach was, for a while, officially abandoned when encrypted SMTP was
+standardized, but many clients kept using it, even as the TCP port number was
+reassigned for other use.
+Thus you may encounter guidance claiming that you shouldn't enable use of
+this port.
+In practice, a number of mail-clients have only supported submissions, not
+submission with STARTTLS upgrade.
+Ideally, offer both submission (587) and submissions (465) service.
+
+Exim supports TLS-on-connect by means of the &%tls_on_connect_ports%&
+global option. Its value must be a list of port numbers;
+the most common use is expected to be:

 .code
 tls_on_connect_ports = 465
 .endd
 .code
 tls_on_connect_ports = 465
 .endd


@@ -27111,7 +27150,7 @@ an extra port &-- rather, it specifies different behaviour on a port that is
 defined elsewhere.
 
 There is also a &%-tls-on-connect%& command line option. This overrides
 defined elsewhere.
 
 There is also a &%-tls-on-connect%& command line option. This overrides

-&%tls_on_connect_ports%&; it forces the legacy behaviour for all ports.
+&%tls_on_connect_ports%&; it forces the TLS-only behaviour for all ports.

 
 
 
 
 
 


@@ -27390,8 +27429,8 @@ tls_require_ciphers = ${if =={$received_port}{25}\
 When Exim has been built with TLS support, it advertises the availability of
 the STARTTLS command to client hosts that match &%tls_advertise_hosts%&,
 but not to any others. The default value of this option is *, which means
 When Exim has been built with TLS support, it advertises the availability of
 the STARTTLS command to client hosts that match &%tls_advertise_hosts%&,
 but not to any others. The default value of this option is *, which means

-that STARTTLS is alway advertised.  Set it to blank to never advertise;
-this is reasonble for systems that want to use TLS only as a client.
+that STARTTLS is always advertised.  Set it to blank to never advertise;
+this is reasonable for systems that want to use TLS only as a client.

 
 If STARTTLS is to be used you
 need to set some other options in order to make TLS available.
 
 If STARTTLS is to be used you
 need to set some other options in order to make TLS available.


@@ -27824,7 +27863,7 @@ unencrypted data stream from and to the delivery processes.
 
 An older mode of operation can be enabled on a per-host basis by the
 &%hosts_noproxy_tls%& option on the &(smtp)& transport.  If the host matches
 
 An older mode of operation can be enabled on a per-host basis by the
 &%hosts_noproxy_tls%& option on the &(smtp)& transport.  If the host matches

-this list the proxy process descibed above is not used; instead Exim
+this list the proxy process described above is not used; instead Exim

 shuts down an existing TLS session being run by the delivery process
 before passing the socket to a new process. The new process may then
 try to start a new TLS session, and if successful, may try to re-authenticate
 shuts down an existing TLS session being run by the delivery process
 before passing the socket to a new process. The new process may then
 try to start a new TLS session, and if successful, may try to re-authenticate


@@ -28271,8 +28310,8 @@ acl_smtp_rcpt = ${if ={25}{$interface_port} \
                      {acl_check_rcpt} {acl_check_rcpt_submit} }
 .endd
 In the default configuration file there are some example settings for
                      {acl_check_rcpt} {acl_check_rcpt_submit} }
 .endd
 In the default configuration file there are some example settings for

-providing an RFC 4409 message submission service on port 587 and a
-non-standard &"smtps"& service on port 465. You can use a string
+providing an RFC 4409 message &"submission"& service on port 587 and
+an RFC 8314 &"submissions"& service on port 465. You can use a string

 expansion like this to choose an ACL for MUAs on these ports which is
 more appropriate for this purpose than the default ACL on port 25.
 
 expansion like this to choose an ACL for MUAs on these ports which is
 more appropriate for this purpose than the default ACL on port 25.
 


@@ -31100,7 +31139,7 @@ This option applies to recipient callouts only. For example:
 .code
 require  verify = recipient/callout=use_sender,hold
 .endd
 .code
 require  verify = recipient/callout=use_sender,hold
 .endd

-It causes the connection to be helod open and used for any further recipients
+It causes the connection to be held open and used for any further recipients

 and for eventual delivery (should that be done quickly).
 Doing this saves on TCP and SMTP startup costs, and TLS costs also
 when that is used for the connections.
 and for eventual delivery (should that be done quickly).
 Doing this saves on TCP and SMTP startup costs, and TLS costs also
 when that is used for the connections.


@@ -32329,7 +32368,7 @@ All parts contained within an attachment multipart are attachments.
 
 As an example, the following will ban &"HTML mail"& (including that sent with
 alternative plain text), while allowing HTML files to be attached. HTML
 
 As an example, the following will ban &"HTML mail"& (including that sent with
 alternative plain text), while allowing HTML files to be attached. HTML

-coverletter mail attached to non-HMTL coverletter mail will also be allowed:
+coverletter mail attached to non-HTML coverletter mail will also be allowed:

 .code
 deny message = HTML mail is not accepted here
 !condition = $mime_is_rfc822
 .code
 deny message = HTML mail is not accepted here
 !condition = $mime_is_rfc822


@@ -36300,7 +36339,7 @@ the &"=>"& line, tagged with S=.
 .new
 .cindex log "DKIM verification"
 .cindex DKIM "verification logging"
 .new
 .cindex log "DKIM verification"
 .cindex DKIM "verification logging"

-&%dkim%&: For message acceptance log lines, when an DKIM signture in the header
+&%dkim%&: For message acceptance log lines, when an DKIM signature in the header

 verifies successfully a tag of DKIM is added, with one of the verified domains.
 .next
 .cindex log "DKIM verification"
 verifies successfully a tag of DKIM is added, with one of the verified domains.
 .next
 .cindex log "DKIM verification"


@@ -36379,7 +36418,7 @@ connection is unexpectedly dropped.
 .next
 .cindex "log" "millisecond timestamps"
 .cindex millisecond logging
 .next
 .cindex "log" "millisecond timestamps"
 .cindex millisecond logging

-.cindex timstamps "millisecond, in logs"
+.cindex timestamps "millisecond, in logs"

 &%millisec%&: Timestamps have a period and three decimal places of finer granularity
 appended to the seconds value.
 .next
 &%millisec%&: Timestamps have a period and three decimal places of finer granularity
 appended to the seconds value.
 .next


@@ -36394,7 +36433,7 @@ followed by IP address in square brackets. You can disable this by turning
 off the &%outgoing_interface%& option.
 .next
 .cindex "log" "outgoing remote port"
 off the &%outgoing_interface%& option.
 .next
 .cindex "log" "outgoing remote port"

-.cindex "port" "logging outgoint remote"
+.cindex "port" "logging outgoing remote"

 .cindex "TCP/IP" "logging outgoing remote port"
 &%outgoing_port%&: The remote port number is added to delivery log lines (those
 containing => tags) following the IP address.
 .cindex "TCP/IP" "logging outgoing remote port"
 &%outgoing_port%&: The remote port number is added to delivery log lines (those
 containing => tags) following the IP address.


@@ -38560,7 +38599,7 @@ There is no dot-stuffing (and no dot-termination).
 DKIM is a mechanism by which messages sent by some entity can be provably
 linked to a domain which that entity controls.  It permits reputation to
 be tracked on a per-domain basis, rather than merely upon source IP address.
 DKIM is a mechanism by which messages sent by some entity can be provably
 linked to a domain which that entity controls.  It permits reputation to
 be tracked on a per-domain basis, rather than merely upon source IP address.

-DKIM is documented in RFC 4871.
+DKIM is documented in RFC 6376.

 
 .new
 As DKIM relies on the message being unchanged in transit, messages handled
 
 .new
 As DKIM relies on the message being unchanged in transit, messages handled


@@ -38622,7 +38661,12 @@ rsa-sha1 MUST NOT be used for signing or verifying.
 Signers MUST use RSA keys of at least 1024 bits for all keys.
 Signers SHOULD use RSA keys of at least 2048 bits.
 .endd
 Signers MUST use RSA keys of at least 1024 bits for all keys.
 Signers SHOULD use RSA keys of at least 2048 bits.
 .endd

-.wen
+
+Note also that the key content (the 'p=' field)
+in the DNS record is different between RSA and EC keys;
+for the former it is the base64 of the ASN.1 for the RSA public key
+(equivalent to the private-key .pem with the header/trailer stripped)
+but for EC keys it is the base64 of the pure key; no ASN.1 wrapping.

 .wen
 
 Signing is enabled by setting private options on the SMTP transport.
 .wen
 
 Signing is enabled by setting private options on the SMTP transport.


@@ -38651,10 +38695,14 @@ You can use the &%$dkim_domain%& and
 &%$dkim_selector%& expansion variables to determine the private key to use.
 The result can either
 .ilist
 &%$dkim_selector%& expansion variables to determine the private key to use.
 The result can either
 .ilist

-be a valid RSA private key in ASCII armor, including line breaks.
+be a valid RSA private key in ASCII armor (.pem file), including line breaks
+.new
+.next
+with GnuTLS 3.6.0 or later, be a valid Ed25519 private key (same format as above)
+.wen

 .next
 start with a slash, in which case it is treated as a file that contains
 .next
 start with a slash, in which case it is treated as a file that contains

-the private key.
+the private key

 .next
 be "0", "false" or the empty string, in which case the message will not
 be signed. This case will not result in an error, even if &%dkim_strict%&
 .next
 be "0", "false" or the empty string, in which case the message will not
 be signed. This case will not result in an error, even if &%dkim_strict%&


@@ -38667,6 +38715,15 @@ Note that RFC 8301 says:
 Signers MUST use RSA keys of at least 1024 bits for all keys.
 Signers SHOULD use RSA keys of at least 2048 bits.
 .endd
 Signers MUST use RSA keys of at least 1024 bits for all keys.
 Signers SHOULD use RSA keys of at least 2048 bits.
 .endd

+
+Support for EC keys is being developed under
+&url(https://datatracker.ietf.org/doc/draft-ietf-dcrup-dkim-crypto/).
+They are considerably smaller than RSA keys for equivalent protection.
+As they are a recent development, users should consider dual-signing
+(by setting a list of selectors, and an expansion for this option)
+for some transition period.
+The "_CRYPTO_SIGN_ED25519" macro will be defined if support is present
+for EC keys.

 .wen
 
 .option dkim_hash smtp string&!! sha256
 .wen
 
 .option dkim_hash smtp string&!! sha256


@@ -38710,7 +38767,7 @@ whether or not each header is present in the message.
 The default list is available for the expansion in the macro
 "_DKIM_SIGN_HEADERS".
 
 The default list is available for the expansion in the macro
 "_DKIM_SIGN_HEADERS".
 

-If a name is repeated, multiple headers by that name (or the absence therof)
+If a name is repeated, multiple headers by that name (or the absence thereof)

 will be signed.  The textually later headers in the headers part of the
 message are signed first, if there are multiples.
 
 will be signed.  The textually later headers in the headers part of the
 message are signed first, if there are multiples.
 


@@ -38718,7 +38775,7 @@ A name can be prefixed with either an '=' or a '+' character.
 If an '=' prefix is used, all headers that are present with this name
 will be signed.
 If a '+' prefix if used, all headers that are present with this name
 If an '=' prefix is used, all headers that are present with this name
 will be signed.
 If a '+' prefix if used, all headers that are present with this name

-will be signed, and one signtature added for a missing header with the
+will be signed, and one signature added for a missing header with the

 name will be appended.
 
 
 name will be appended.
 
 


@@ -38849,6 +38906,11 @@ The key record selector string.
 
 .vitem &%$dkim_algo%&
 The algorithm used. One of 'rsa-sha1' or 'rsa-sha256'.
 
 .vitem &%$dkim_algo%&
 The algorithm used. One of 'rsa-sha1' or 'rsa-sha256'.

+.new
+If running under GnuTLS 3.6.0 or later, may also be 'ed25519-sha256'.
+The "_CRYPTO_SIGN_ED25519" macro will be defined if support is present
+for EC keys.
+.wen

 
 .new
 Note that RFC 8301 says:
 
 .new
 Note that RFC 8301 says:


@@ -39390,7 +39452,7 @@ the "headers charset" command (in a filter file)
 or &%headers_charset%& main configuration option (otherwise),
 to the
 modified UTF-7 encoding specified by RFC 2060,
 or &%headers_charset%& main configuration option (otherwise),
 to the
 modified UTF-7 encoding specified by RFC 2060,

-with the following exception: All occurences of <sep>
+with the following exception: All occurrences of <sep>

 (which has to be a single character)
 are replaced with periods ("."), and all periods and slashes that are not
 <sep> and are not in the <specials> string are BASE64 encoded.
 (which has to be a single character)
 are replaced with periods ("."), and all periods and slashes that are not
 <sep> and are not in the <specials> string are BASE64 encoded.


@@ -39476,7 +39538,7 @@ The second column in the table above describes whether the event fires
 before or after the action is associates with.  Those which fire before
 can be used to affect that action (more on this below).
 
 before or after the action is associates with.  Those which fire before
 can be used to affect that action (more on this below).
 

-The third column in the table above says what section of the configumration
+The third column in the table above says what section of the configuration

 should define the event action.
 
 An additional variable, &$event_data$&, is filled with information varying
 should define the event action.
 
 An additional variable, &$event_data$&, is filled with information varying