waiting for it by the time it recovers, and sending them in a single SMTP
connection is clearly beneficial. Whenever a delivery to a remote host is
deferred,
-.cindex "hints database"
+.cindex "hints database" "deferred deliveries"
Exim makes a note in its hints database, and whenever a successful
SMTP delivery has happened, it looks to see if any other messages are waiting
for the same host. If any are found, they are sent over the same SMTP
Exim's configuration file is divided into a number of different parts. General
option settings must always appear at the start of the file. The other parts
are all optional, and may appear in any order. Each part other than the first
-is introduced by the word &"begin"& followed by the name of the part. The
-optional parts are:
+is introduced by the word &"begin"& followed by at least one literal
+space, and the name of the part. The optional parts are:
.ilist
&'ACL'&: Access control lists for controlling incoming SMTP mail (see chapter
set a server-side limit on the time taken to complete a search.
The SERVERS parameter allows you to specify an alternate list of ldap servers
-to use for an individual lookup. The global ldap_servers option provides a
+to use for an individual lookup. The global &%ldap_default_servers%& option provides a
default list of ldap servers, and a single lookup can specify a single ldap
server to use. But when you need to do a lookup with a list of servers that is
different than the default list (maybe different order, maybe a completely
found, but that is still a successful query. In other words, the list of
servers provides a backup facility, not a list of different places to look.
+.new
The &%quote_mysql%&, &%quote_pgsql%&, and &%quote_oracle%& expansion operators
convert newline, tab, carriage return, and backspace to \n, \t, \r, and \b
respectively, and the characters single-quote, double-quote, and backslash
-itself are escaped with backslashes. The &%quote_pgsql%& expansion operator, in
-addition, escapes the percent and underscore characters. This cannot be done
-for MySQL because these escapes are not recognized in contexts where these
-characters are not special.
+itself are escaped with backslashes.
+.wen
.section "Specifying the server in the query" "SECTspeserque"
For MySQL and PostgreSQL lookups (but not currently for Oracle and InterBase),
qualified host name. See also &$smtp_active_hostname$&.
+.new
+.vitem &$prdr_requested$&
+.cindex "PRDR" "variable for"
+This variable is set to &"yes"& if PRDR was requested by the client for the
+current message, otherwise &"no"&.
+.wen
+
.vitem &$prvscheck_address$&
This variable is used in conjunction with the &%prvscheck%& expansion item,
which is described in sections &<<SECTexpansionitems>>& and
to ensure that any additional groups associated with the uid are set up.
+.new
+.option max_parallel transports integer&!! unset
+.cindex limit "transport parallelism"
+.cindex transport "parallel processes"
+.cindex transport "concurrency limit"
+.cindex "delivery" "parallelism for transport"
+If this option is set and expands to an integer greater than zero
+it limits the number of concurrent runs of the transport.
+The control does not apply to shadow transports.
+
+.cindex "hints database" "transport concurrency control"
+Exim implements this control by means of a hints database in which a record is
+incremented whenever a transport process is beaing created. The record
+is decremented and possibly removed when the process terminates.
+Obviously there is scope for
+records to get left lying around if there is a system or program crash. To
+guard against this, Exim ignores any records that are more than six hours old.
+
+If you use this option, you should also arrange to delete the
+relevant hints database whenever your system reboots. The names of the files
+start with &_misc_& and they are kept in the &_spool/db_& directory. There
+may be one or two files, depending on the type of DBM in use. The same files
+are used for ETRN and smtp transport serialization.
+.wen
+
+
.option message_size_limit transports string&!! 0
.cindex "limit" "message size per transport"
.cindex "size" "of message, limit"
This option sets up a filtering (in the Unix shell sense) process for messages
at transport time. It should not be confused with mail filtering as set up by
individual users or via a system filter.
+.new
+If unset, or expanding to an empty string, no filtering is done.
+.wen
When the message is about to be written out, the command specified by
&%transport_filter%& is started up in a separate, parallel process, and
delivery, the two pipe transports may be run concurrently. You must ensure that
any pipe commands you set up are robust against this happening. If the commands
write to a file, the &%exim_lock%& utility might be of use.
+.new
+Alternatively the &%max_parallel%& option could be used with a value
+of "1" to enforce serialization.
+.wen
may be one or two files, depending on the type of DBM in use. The same files
are used for ETRN serialization.
+.new
+See also the &%max_parallel%& generic transport option.
+.wen
+
.option size_addition smtp integer 1024
.cindex "SMTP" "SIZE"
PRDR may be used to support per-user content filtering. Without it
one must defer any recipient after the first that has a different
content-filter configuration. With PRDR, the RCPT-time check
-for this can be disabled when the MAIL-time $smtp_command included
-"PRDR". Any required difference in behaviour of the main DATA-time
+.new
+.cindex "PRDR" "variable for"
+for this can be disabled when the variable &$prdr_requested$&
+is &"yes"&.
+.wen
+Any required difference in behaviour of the main DATA-time
ACL should however depend on the PRDR-time ACL having run, as Exim
will avoid doing so in some situations (e.g. single-recipient mails).
Elements after the first for Unix sockets, or second for TCP socket,
are options.
-The supported option are:
+The supported options are:
.code
pri=<priority> Selection priority
weight=<value> Selection bias
.next
Serializing delivery to a specific host (when &%serialize_hosts%& is set in an
&(smtp)& transport)
+.next
+Limiting the concurrency of specific transports (when &%max_parallel%& is set
+in a transport)
.endlist