of domains that it defines.
.next
.vindex "&$local_part_prefix$&"
+.vindex "&$local_part_prefix_v$&"
.vindex "&$local_part$&"
.vindex "&$local_part_suffix$&"
+.vindex "&$local_part_suffix_v$&"
.cindex affix "router precondition"
If the &%local_parts%& option is set, the local part of the address must be in
the set of local parts that it defines. If &%local_part_prefix%& or
&%local_part_suffix%& is in use, the prefix or suffix is removed from the local
part before this check. If you want to do precondition tests on local parts
that include affixes, you can do so by using a &%condition%& option (see below)
-that uses the variables &$local_part$&, &$local_part_prefix$&, and
-&$local_part_suffix$& as necessary.
+.new
+that uses the variables &$local_part$&, &$local_part_prefix$&,
+&$local_part_prefix_v$&, &$local_part_suffix$&
+and &$local_part_suffix_v$& as necessary.
+.wen
.next
.vindex "&$local_user_uid$&"
.vindex "&$local_user_gid$&"
by Exim in conjunction with the &%-MC%& option. It signifies that the
remote host supports the ESMTP &_DSN_& extension.
+.new
+.vitem &%-MCd%&
+.oindex "&%-MCd%&"
+This option is not intended for use by external callers. It is used internally
+by Exim in conjunction with the &%-d%& option
+to pass on an information string on the purpose of the process.
+.wen
+
.vitem &%-MCG%&&~<&'queue&~name'&>
.oindex "&%-MCG%&"
This option is not intended for use by external callers. It is used internally
.vitem &%-MG%&&~<&'queue&~name'&>&~<&'message&~id'&>&~<&'message&~id'&>&~...
.oindex "&%-MG%&"
.cindex queue named
-.cindex "named queues"
+.cindex "named queues" "moving messages"
.cindex "queue" "moving messages"
This option requests that each listed message be moved from its current
queue to the given named queue.
.vitem &%-odqs%&
.oindex "&%-odqs%&"
.cindex "SMTP" "delaying delivery"
+.cindex "first pass routing"
This option is a hybrid between &%-odb%&/&%-odi%& and &%-odq%&.
However, like &%-odb%& and &%-odi%&, this option has no effect if
&%queue_only_override%& is false and one of the queueing options in the
.cindex "queue" "double scanning"
.cindex "queue" "routing"
.cindex "routing" "whole queue before delivery"
+.cindex "first pass routing"
An option starting with &%-qq%& requests a two-stage queue run. In the first
stage, the queue is scanned as if the &%queue_smtp_domains%& option matched
every domain. Addresses are routed, local deliveries happen, but no remote
transports are run.
+.new
+Performance will be best if the &%queue_run_in_order%& option is false.
+.wen
+
.cindex "hints database" "remembering routing"
The hints database that remembers which messages are waiting for specific hosts
is updated, as if delivery to those hosts had been deferred. After this is
.vitem &%-q[q][i][f[f]][l][G<name>[/<time>]]]%&
.oindex "&%-qG%&"
.cindex queue named
-.cindex "named queues"
+.cindex "named queues" "deliver from"
.cindex "queue" "delivering specific messages"
If the &'G'& flag and a name is present, the queue runner operates on the
queue with the given name rather than the default queue.
whose name is the key by calling the &[lstat()]& function. The key may not
contain any forward slash characters. If &[lstat()]& succeeds, the result of
the lookup is the name of the entry, which may be a file, directory,
-symbolic link, or any other kind of directory entry. An example of how this
+symbolic link, or any other kind of directory entry.
+.new
+.cindex "tainted data" "dsearch result"
+It is regarded as untainted.
+.wen
+An example of how this
lookup can be used to support virtual domains is given in section
&<<SECTvirtualdomains>>&.
.next
where &'x.y'& does not match. It's best to avoid negation altogether in
referenced lists if you can.
+.new
+.cindex "hiding named list values"
+.cindex "named lists" "hiding value of"
+Some named list definitions may contain sensitive data, for example, passwords for
+accessing databases. To stop non-admin users from using the &%-bP%& command
+line option to read these values, you can precede the definition with the
+word &"hide"&. For example:
+.code
+hide domainlist filter_for_domains = ldap;PASS=secret ldap::/// ...
+.endd
+.wen
+
+
Named lists may have a performance advantage. When Exim is routing an
address or checking an incoming message, it caches the result of tests on named
lists. So, if you have a setting such as
"&*$bheader_*&<&'header&~name'&>&*:*&&~or&~&&&
&*$bh_*&<&'header&~name'&>&*:*&" &&&
"&*$lheader_*&<&'header&~name'&>&*:*&&~or&~&&&
- &*$lh_*&<&'header&~name'&>&*:*&"
+ &*$lh_*&<&'header&~name'&>&*:*&" &&&
"&*$rheader_*&<&'header&~name'&>&*:*&&~or&~&&&
&*$rh_*&<&'header&~name'&>&*:*&"
.cindex "expansion" "header insertion"
.wen
.vindex "&$local_part_prefix$&"
+.vindex "&$local_part_prefix_v$&"
.vindex "&$local_part_suffix$&"
+.vindex "&$local_part_suffix_v$&"
.cindex affix variables
If a local part prefix or suffix has been recognized, it is not included in the
value of &$local_part$& during routing and subsequent delivery. The values of
any prefix or suffix are in &$local_part_prefix$& and
&$local_part_suffix$&, respectively.
+.new
+If the affix specification included a wildcard then the portion of
+the affix matched by the wildcard is in
+&$local_part_prefix_v$& or &$local_part_suffix_v$& as appropriate.
+.wen
When a message is being delivered to a file, pipe, or autoreply transport as a
result of aliasing or forwarding, &$local_part$& is set to the local part of
specific prefix for the local part was recognized, it is available in this
variable, having been removed from &$local_part$&.
+.new
+.vitem &$local_part_prefix_v$&
+.vindex "&$local_part_prefix_v$&"
+When &$local_part_prefix$& is valid and the prefix match used a wildcard,
+the portion matching the wildcard is available in this variable.
+.wen
+
.vitem &$local_part_suffix$&
.vindex "&$local_part_suffix$&"
When an address is being routed or delivered, and a
specific suffix for the local part was recognized, it is available in this
variable, having been removed from &$local_part$&.
+.new
+.vitem &$local_part_suffix_v$&
+.vindex "&$local_part_suffix_v$&"
+When &$local_part_suffix$& is valid and the suffix match used a wildcard,
+the portion matching the wildcard is available in this variable.
+.wen
+
.new
.vitem &$local_part_verified$&
.vindex "&$local_part_verified$&"
.vitem &$queue_name$&
.vindex &$queue_name$&
-.cindex "named queues"
+.cindex "named queues" variable
.cindex queues named
The name of the spool queue in use; empty for the default queue.
+.vitem &$queue_size$&
+.vindex "&$queue_size$&"
+.cindex "queue" "size of"
+.cindex "spool" "number of messages"
+This variable contains the number of messages queued.
+It is evaluated on demand, but no more often than once every minute.
+
.vitem &$r_...$&
.vindex &$r_...$&
.cindex router variables
.row &%daemon_startup_sleep%& "time to sleep between tries"
.row &%extra_local_interfaces%& "not necessarily listened on"
.row &%local_interfaces%& "on which to listen, with optional ports"
+.row &%notifier_socket%& "override compiled-in value"
.row &%pid_file_path%& "override compiled-in value"
.row &%queue_run_max%& "maximum simultaneous queue runners"
.endtable
transport driver.
+.new
+.option notifier_socket main string "$spool_directory/exim_daemon_notify"
+This option gives the name for a unix-domain socket on which the daemon
+listens for work and information-requests.
+Only installations running multiple daemons sharing a spool directory
+should need to modify the default.
+
+The option is expanded before use.
+If the platform supports Linux-style abstract socket names, the result
+is used with a nul byte prefixed.
+Otherwise, it should be a full path name and use a directory accessible
+to Exim.
+
+If the Exim command line uses a &%-oX%& option and does not use &%-oP%&
+then a notifier socket is not created.
+.wen
+
+
.option openssl_options main "string list" "+no_sslv2 +no_sslv3 +single_dh_use +no_ticket +no_renegotiation"
.cindex "OpenSSL "compatibility options"
This option allows an administrator to adjust the SSL options applied
the daemon's command line.
.cindex queues named
-.cindex "named queues"
+.cindex "named queues" "resource limit"
To set limits for different named queues use
an expansion depending on the &$queue_name$& variable.
.option queue_smtp_domains main "domain list&!!" unset
.cindex "queueing incoming messages"
.cindex "message" "queueing remote deliveries"
+.cindex "first pass routing"
When this option is set, a delivery process is started whenever a message is
received, routing is performed, and local deliveries take place.
However, if any SMTP deliveries are required for domains that match
smtp_etrn_command = /etc/etrn_command $domain \
$sender_host_address
.endd
+.new
+If the option is not set, the argument for the ETRN command must
+be a &'#'& followed by an address string.
+In this case an &'exim -R <string>'& command is used;
+if the ETRN ACL has set up a named-queue then &'-MCG <queue>'& is appended.
+.wen
+
A new process is created to run the command, but Exim does not wait for it to
complete. Consequently, its status cannot be checked. If the command cannot be
run, a line is written to the panic log, but the ETRN caller still receives
This option specifies a list of text headers,
colon-separated (by default, changeable in the usual way &<<SECTlistsepchange>>&),
that is associated with any addresses that are accepted by the router.
-Each item is separately expanded, at routing time. However, this
-option has no effect when an address is just being verified. The way in which
+However, the option has no effect when an address is just being verified.
+Each list item is separately expanded, at transport time.
+.new
+If an item ends in *, it will match any header with the given prefix.
+.wen
+The way in which
the text is used to remove header lines at transport time is described in
section &<<SECTheadersaddrem>>&. Header lines are not actually removed until
the message is in the process of being transported. This means that references
to header lines in string expansions in the transport's configuration still
&"see"& the original header lines.
-The &%headers_remove%& option is expanded after &%errors_to%& and
+The &%headers_remove%& option is handled after &%errors_to%& and
&%headers_add%&, but before &%transport%&. If an item expansion is forced to fail,
the item has no effect. Other expansion failures are treated as configuration
errors.
This behaviour can be overridden by setting &%rcpt_include_affixes%& true on
the relevant transport.
+.new
+.vindex &$local_part_prefix_v$&
+If wildcarding (above) was used then the part of the prefix matching the
+wildcard is available in &$local_part_prefix_v$&.
+.wen
+
When an address is being verified, &%local_part_prefix%& affects only the
behaviour of the router. If the callout feature of verification is in use, this
means that the full address, including the prefix, will be used during the
.section "Format of one host item" "SECTformatonehostitem"
-Each item in the list of hosts is either a host name or an IP address,
-optionally with an attached port number. When no port is given, an IP address
+Each item in the list of hosts can be either a host name or an IP address,
+optionally with an attached port number, or it can be a single "+"
+(see &%hosts_randomize%&).
+When no port is given, an IP address
is not enclosed in brackets. When a port is specified, it overrides the port
specification on the transport. The port is separated from the name or address
by a colon. This leads to some complications:
comments.
.new
+.cindex "tainted data" "in filenames"
+.cindex redirect "tainted data"
+Tainted data may not be used for a filename.
+
&*Warning*&: It is unwise to use &$local_part$& or &$domain$&
directly for redirection,
as they are provided by a potential attacker.
.code
list1: :include:/opt/lists/list1
.endd
+.new
+.cindex "tainted data" "in filenames"
+.cindex redirect "tainted data"
+Tainted data may not be used for a filename.
+.wen
.next
.cindex "address redirection" "to black hole"
.cindex "delivery" "discard"
.option headers_remove transports list&!! unset
.cindex "header lines" "removing"
.cindex "transport" "header lines; removing"
-This option specifies a list of header names,
-colon-separated (by default, changeable in the usual way &<<SECTlistsepchange>>&);
-these headers are omitted from the message as it is transported, as described
-in section &<<SECTheadersaddrem>>&. Header removal can also be specified by
-routers.
+This option specifies a list of text headers,
+colon-separated (by default, changeable in the usual way &<<SECTlistsepchange>>&),
+to be removed from the message.
+However, the option has no effect when an address is just being verified.
Each list item is separately expanded.
If the result of the expansion is an empty string, or if the expansion
is forced to fail, no action is taken. Other expansion failures are treated as
errors and cause the delivery to be deferred.
+.new
+If an item ends in *, it will match any header with the given prefix.
+.wen
+
+Matching headers are omitted from the message as it is transported, as described
+in section &<<SECTheadersaddrem>>&. Header removal can also be specified by
+routers.
Unlike most options, &%headers_remove%& can be specified multiple times
for a transport; all listed headers are removed.
.section "The PLAIN authentication mechanism" "SECID172"
.cindex "PLAIN authentication mechanism"
-.cindex "authentication" "PLAIN mechanism"
+.cindex authentication PLAIN
.cindex "binary zero" "in &(plaintext)& authenticator"
The PLAIN authentication mechanism (RFC 2595) specifies that three strings be
sent as one item of data (that is, one combined string containing two NUL
.section "The LOGIN authentication mechanism" "SECID173"
.cindex "LOGIN authentication mechanism"
-.cindex "authentication" "LOGIN mechanism"
+.cindex authentication LOGIN
The LOGIN authentication mechanism is not documented in any RFC, but is in use
in a number of programs. No data is sent with the AUTH command. Instead, a
user name and password are supplied separately, in response to prompts. The
.scindex IIDcramauth1 "&(cram_md5)& authenticator"
.scindex IIDcramauth2 "authenticators" "&(cram_md5)&"
.cindex "CRAM-MD5 authentication mechanism"
-.cindex "authentication" "CRAM-MD5 mechanism"
+.cindex authentication CRAM-MD5
The CRAM-MD5 authentication mechanism is described in RFC 2195. The server
sends a challenge string to the client, and the response consists of a user
name and the CRAM-MD5 digest of the challenge string combined with a secret
.cindex "authentication" "LOGIN"
.cindex "authentication" "DIGEST-MD5"
.cindex "authentication" "CRAM-MD5"
-.cindex "authentication" "SCRAM-SHA-1"
-.cindex "authentication" "SCRAM-SHA-1-PLUS"
-.cindex "authentication" "SCRAM-SHA-256"
-.cindex "authentication" "SCRAM-SHA-256-PLUS"
+.cindex "authentication" "SCRAM family"
The &(gsasl)& authenticator provides integration for the GNU SASL
library and the mechanisms it provides. This is new as of the 4.80 release
and there are a few areas where the library does not let Exim smoothly
the account name to be used.
.wen
+.new
+.option client_spassword gsasl string&!! unset
+If a SCRAM mechanism is being used and this option is set
+it is used in preference to &%client_password%&.
+The value after expansion should be
+a 40 (for SHA-1) or 64 (for SHA-256) character string
+with the PBKDF2-prepared password, hex-encoded.
+Note that this value will depend on the salt and iteration-count
+supplied by the server.
+.wen
+
+
+
.option server_channelbinding gsasl boolean false
Do not set this true and rely on the properties
without consulting a cryptographic engineer.
.option server_scram_iter gsasl string&!! 4096
This option provides data for the SCRAM family of mechanisms.
.new
-The &$auth1$&, &$auth2$& and &$auth3$& variables are available for expansion.
+The &$auth1$&, &$auth2$& and &$auth3$& variables are available
+when this option is expanded.
The result of expansion should be a decimal number,
and represents both a lower-bound on the security, and
(if it does not cache results, or the server changes
either the iteration count or the salt).
A minimum value of 4096 is required by the standards
-for all current CRAM mechanism variants.
+for all current SCRAM mechanism variants.
.wen
-
.option server_scram_salt gsasl string&!! unset
This option provides data for the SCRAM family of mechanisms.
.new
-The &$auth1$&, &$auth2$& and &$auth3$& variables are available for expansion.
+The &$auth1$&, &$auth2$& and &$auth3$& variables are available
+when this option is expanded.
+The value should be a base64-encoded string,
+of random data typically 4-to-16 bytes long.
If unset or empty after expansion the library will provides a value for the
protocol conversation.
.wen
+.new
+.option server_key gsasl string&!! unset
+.option server_skey gsasl string&!! unset
+These options can be used for the SCRAM family of mechanisms
+to provide stored information related to a password,
+the storage of which is preferable to plaintext.
+
+&%server_key%& is the value defined in the SCRAM standards as ServerKey;
+&%server_skey%& is StoredKey.
+
+They are only available for version 1.9.0 (or later) of the gsasl library.
+When this is so, the macros
+_OPT_AUTHENTICATOR_GSASL_SERVER_KEY
+and _HAVE_AUTH_GSASL_SCRAM_S_KEY
+will be defined.
+
+The &$authN$& variables are available when these options are expanded.
+
+If set, the results of expansion should for each
+should be a 28 (for SHA-1) or 44 (for SHA-256) character string
+of base64-coded data, and will be used in preference to the
+&%server_password%& option.
+If unset or not of the right length, &%server_password%& will be used.
+
+The libgsasl library release includes a utility &'gsasl'& which can be used
+to generate these values.
+.wen
+
+
.option server_service gsasl string &`smtp`&
This is the SASL service that the server claims to implement.
Some mechanisms will use this data.
It can be at the end of an &%accept%& statement:
.code
accept ...some conditions
- control = queue_only
+ control = queue
.endd
In this case, the control is applied when this statement yields &"accept"&, in
other words, when the conditions are all true.
It can be in the middle of an &%accept%& statement:
.code
accept ...some conditions...
- control = queue_only
+ control = queue
...some more conditions...
.endd
If the first set of conditions are true, the control is applied, even if the
controlled by &%acl_smtp_connect%& or &%acl_smtp_helo%&. See also
&%pipelining_advertise_hosts%&.
-.vitem &*control&~=&~queue_only*&
+.new
+.vitem &*control&~=&~queue/*&<&'options'&>* &&&
+ &*control&~=&~queue_only*&
+.oindex "&%queue%&"
.oindex "&%queue_only%&"
.cindex "queueing incoming messages"
+.cindex queueing "forcing in ACL"
+.cindex "first pass routing"
This control is permitted only for the MAIL, RCPT, DATA, and non-SMTP ACLs, in
other words, only when a message is being received. If the message is accepted,
it is placed on Exim's queue and left there for delivery by a subsequent queue
-runner. No immediate delivery process is started. In other words, it has the
-effect as the &%queue_only%& global option. However, the control applies only
-to the current message, not to any subsequent ones that may be received in the
-same SMTP connection.
+runner.
+If used with no options set,
+no immediate delivery process is started. In other words, it has the
+effect as the &%queue_only%& global option or &'-odq'& command-line option.
+
+If the &'first_pass_route'& option is given then
+the behaviour is like the command-line &'-oqds'& option;
+a delivery process is started which stops short of making
+any SMTP delivery. The benefit is that the hints database will be updated for
+the message being waiting for a specific host, and a later queue run will be
+able to send all such messages on a single connection.
+
+The control only applies to the current message, not to any subsequent ones that
+ may be received in the same SMTP connection.
+.wen
.vitem &*control&~=&~submission/*&<&'options'&>
.cindex "message" "submission"
available in the MIME ACL:
.vlist
+.vitem &$mime_anomaly_level$& &&&
+ &$mime_anomaly_text$&
+.vindex &$mime_anomaly_level$&
+.vindex &$mime_anomaly_text$&
+If there are problems decoding, these variables contain information on
+the detected issue.
+
.vitem &$mime_boundary$&
-If the current part is a multipart (see &$mime_is_multipart$&) below, it should
+.vindex &$mime_boundary$&
+If the current part is a multipart (see &$mime_is_multipart$& below), it should
have a boundary string, which is stored in this variable. If the current part
has no boundary parameter in the &'Content-Type:'& header, this variable
contains the empty string.
.vitem &$mime_charset$&
+.vindex &$mime_charset$&
This variable contains the character set identifier, if one was found in the
&'Content-Type:'& header. Examples for charset identifiers are:
.code
case-insensitively.
.vitem &$mime_content_description$&
+.vindex &$mime_content_description$&
This variable contains the normalized content of the &'Content-Description:'&
header. It can contain a human-readable description of the parts content. Some
implementations repeat the filename for attachments here, but they are usually
only used for display purposes.
.vitem &$mime_content_disposition$&
+.vindex &$mime_content_disposition$&
This variable contains the normalized content of the &'Content-Disposition:'&
header. You can expect strings like &"attachment"& or &"inline"& here.
.vitem &$mime_content_id$&
+.vindex &$mime_content_id$&
This variable contains the normalized content of the &'Content-ID:'& header.
This is a unique ID that can be used to reference a part from another part.
.vitem &$mime_content_size$&
+.vindex &$mime_content_size$&
This variable is set only after the &%decode%& modifier (see above) has been
successfully run. It contains the size of the decoded part in kilobytes. The
size is always rounded up to full kilobytes, so only a completely empty part
has a &$mime_content_size$& of zero.
.vitem &$mime_content_transfer_encoding$&
+.vindex &$mime_content_transfer_encoding$&
This variable contains the normalized content of the
&'Content-transfer-encoding:'& header. This is a symbolic name for an encoding
type. Typical values are &"base64"& and &"quoted-printable"&.
.vitem &$mime_content_type$&
+.vindex &$mime_content_type$&
If the MIME part has a &'Content-Type:'& header, this variable contains its
value, lowercased, and without any options (like &"name"& or &"charset"&). Here
are some examples of popular MIME types, as they may appear in this variable:
empty string.
.vitem &$mime_decoded_filename$&
+.vindex &$mime_decoded_filename$&
This variable is set only after the &%decode%& modifier (see above) has been
successfully run. It contains the full path and filename of the file
containing the decoded data.
.cindex "RFC 2047"
.vlist
.vitem &$mime_filename$&
+.vindex &$mime_filename$&
This is perhaps the most important of the MIME variables. It contains a
proposed filename for an attachment, if one was found in either the
&'Content-Type:'& or &'Content-Disposition:'& headers. The filename will be
found, this variable contains the empty string.
.vitem &$mime_is_coverletter$&
+.vindex &$mime_is_coverletter$&
This variable attempts to differentiate the &"cover letter"& of an e-mail from
attached data. It can be used to clamp down on flashy or unnecessarily encoded
content in the cover letter, while not restricting attachments at all.
condition = $mime_is_coverletter
condition = ${if eq{$mime_content_type}{text/html}{1}{0}}
.endd
+
.vitem &$mime_is_multipart$&
+.vindex &$mime_is_multipart$&
This variable has the value 1 (true) when the current part has the main type
&"multipart"&, for example, &"multipart/alternative"& or &"multipart/mixed"&.
Since multipart entities only serve as containers for other parts, you may not
want to carry out specific actions on them.
.vitem &$mime_is_rfc822$&
+.vindex &$mime_is_rfc822$&
This variable has the value 1 (true) if the current part is not a part of the
checked message itself, but part of an attached message. Attached message
decoding is fully recursive.
.vitem &$mime_part_count$&
+.vindex &$mime_part_count$&
This variable is a counter that is raised for each processed MIME part. It
starts at zero for the very first part (which is usually a multipart). The
counter is per-message, so it is reset when processing RFC822 attachments (see
.cindex &%dlfunc%& "API description"
You must include this line near the start of your code:
.code
+#define LOCAL_SCAN
#include "local_scan.h"
.endd
This header file defines a number of variables and other values, and the
prototype for the function itself. Exim is coded to use unsigned char values
almost exclusively, and one of the things this header defines is a shorthand
for &`unsigned char`& called &`uschar`&.
-It also contains the following macro definitions, to simplify casting character
+It also makes available the following macro definitions, to simplify casting character
strings and pointers to character strings:
.code
#define CS (char *)
virtual:
driver = redirect
domains = dsearch;/etc/mail/virtual
- data = ${lookup{$local_part}lsearch{/etc/mail/virtual/$domain}}
+ data = ${lookup{$local_part}lsearch{/etc/mail/virtual/$domain_data}}
no_more
.endd
+.new
The &%domains%& option specifies that the router is to be skipped, unless there
is a file in the &_/etc/mail/virtual_& directory whose name is the same as the
-domain that is being processed. When the router runs, it looks up the local
+domain that is being processed.
+The &(dsearch)& lookup used results in an untainted version of &$domain$&
+being placed into the &$domain_data$& variable.
+.wen
+
+When the router runs, it looks up the local
part in the file to find a new address (or list of addresses). The &%no_more%&
setting ensures that if the lookup fails (leading to &%data%& being an empty
string), Exim gives up on the address without trying any subsequent routers.
.cindex "SMTP" "passed connection"
.cindex "SMTP" "multiple deliveries"
.cindex "multiple SMTP deliveries"
+.cindex "first pass routing"
Mail waiting to be sent from an intermittently connected host will probably
not have been routed, because without a connection DNS lookups are not
possible. This means that if a normal queue run is done at connection time,
openssl genrsa -out dkim_rsa.private 2048
openssl rsa -in dkim_rsa.private -out /dev/stdout -pubout -outform PEM
.endd
+The result file from the first command should be retained, and
+this option set to use it.
Take the base-64 lines from the output of the second command, concatenated,
for the DNS TXT record.
See section 3.6 of RFC6376 for the record specification.