Red Hat Linux 7.2 Bible, Unlimited ed phần 8 pps

Configuring sendmail If you ever find the need to strike up a conversation with a system administrator, simply mention “sendmail.cf file,” “address rewriting rules,” or “mail loops back to itself,” and you will be instantly understood, considered a compatriot, and find yourself the recipient of much sympathy. The sendmail.cf file (or sendmail configuration file) is legendary (and infamous) for arcane syntax, nearly indecipherable rule sets, and its capability to make an administrator tear out his or her hair. In reality, some of this reputation is earned and well deserved, but configuring sendmail has gotten much easier in the past few years with the advent of m4 preprocessor macros, which are discussed at the end of this section. Even better, the default /etc/sendmail.cf file that is included in the sendmail RPM will likely work without modification, although a small amount of tweaking should be performed anyway. The file /etc/sendmail.cf contains the configuration information and optional values used to direct the behavior of the sendmail daemon. The entire file is well over 1,000 lines in length, at least half of which are not discussed here (and you are to be pitied if you ever find the need to manipulate those lines). Some potentially useful lines are presented in the sections that follow, with comments interjected after related blocks of options. The generic format of the sendmail.cf file is a single−letter command followed by a parameter (usually represented by a single letter, although not necessarily). For example, options are preceded by a capital O (for option). If a value is required, this is specified last. The command must start in the first column of the line, because leading white space indicates a continuation of the previous line. Also, only one command may exist on a single line. The valid commands are described in Table 19−3. Lines that begin with a # are considered comments and are not processed. Table 19−3: Commands Available in /etc/sendmail.cf Command Description C Defines a “class macro,” a variable that can contain several values. D Defines a macro, which may contain only one value. E Sets an environment variable. F Defines a “file class macro” where the values are obtained from a file or pipe. H Selects the format of a header line. K Declares a keyed database file. L Allows processing restrictions based on the system load average. M Defines an MDA and its parameters. O Assigns a value to an option. P Defines a message priority level. R Assembles a rewriting rule. S Begins a set of rewriting rules. T Classifies a user as “trusted”. V Defines the major version of the configuration file. Because setting up a working sendmail.cf file is the key to getting your e−mail service working, the following sections are devoted to breaking this file down, line by line. If you are setting up your first e−mail server, you should go through these sections thoroughly so that you understand how sendmail works and what you need to change to suit your e−mail configuration. The option lines are discussed first, followed by the discussions of the m4 preprocessor, forward files, and alias files. Note Any line in the sendmail.cf file that begins with a number sign (#) is a comment and is not interpreted. Often, you can uncomment and change these lines to activate a particular feature, as described in the next sections. sendmail component files The first part of the sendmail.cf file contains a listing of component files used to create the sendmail.cf file. It also contains information about the configuration file’s format and version. The following is an example of the beginning of the sendmail.cf file: # # Copyright (c) 1998−2001 Sendmail, Inc. and its suppliers. # All rights reserved. # Copyright (c) 1983, 1995 Eric P. Allman. All rights reserved. # Copyright (c) 1988, 1993 # The Regents of the University of California. All rights reserved. # # By using this file, you agree to the terms and conditions set # forth in the LICENSE file which can be found at the top level of # the sendmail distribution. # # ###################################################################### ###################################################################### ##### ##### SENDMAIL CONFIGURATION FILE ##### ###################################################################### ###################################################################### ##### $Id: cfhead.m4,v 8.76.4.16 2001/03/06 22:56:36 ca Exp $ ##### ##### $Id: cf.m4,v 8.32 1999/02/07 07:26:14 gshapiro Exp $ ##### ##### linux setup for Red Hat Linux ##### ##### $Id: linux.m4,v 8.11.16.2 2000/09/17 17:04:22 gshapiro Exp $ ##### ##### $Id: local_procmail.m4,v 8.21 1999/11/18 05:06:23 ca Exp $ ##### ##### $Id: no_default_msa.m4,v 8.1.10.1 2000/09/17 17:04:22 gs Exp $ ##### ##### $Id: smrsh.m4,v 8.14 1999/11/18 05:06:23 ca Exp $ ##### ##### $Id: mailertable.m4,v 8.18 1999/07/22 17:55:35 gshapiro Exp $ ##### ##### $Id: virtusertable.m4,v 8.16 1999/07/22 17:55:36 gshapiro Exp $ ##### ##### $Id: redirect.m4,v 8.15 1999/08/06 01:47:36 gshapiro Exp $ ##### ##### $Id: always_add_domain.m4,v 8.9 1999/02/07 07:26:08 gshapiro Exp $ ##### ##### $Id: use_cw_file.m4,v 8.9 1999/02/07 07:26:13 gshapiro Exp $ ##### ##### $Id: use_ct_file.m4,v 8.9 1999/02/07 07:26:13 gshapiro Exp $ ##### ##### $Id: local_procmail.m4,v 8.21 1999/11/18 05:06:23 ca Exp $ ##### ##### $Id: access_db.m4,v 8.15 1999/07/22 17:55:34 gshapiro Exp $ ##### ##### $Id: blacklist_recipients.m4,v 8.13 1999/04/02 02:25:13 gs Exp $ ##### ##### $Id: accept_unresolvable_domains.m4,v 8.10 1999/02/0707:26:07 gs Exp$ ## ##### $Id: proto.m4,v 8.446.2.5.2.41 2001/05/23 21:32:16 ca Exp $ ##### The preceding block of comments is useful, because it indicates which component m4 macro files (from within subdirectories of the /usr/lib/sendmail−cf directory) were used to create this sendmail.cf file. The /etc/sendmail.mc file is the actual configuration file used to build sendmail.cf (using the command m4 /etc/sendmail.mc > /etc/sendmail.cf). The following code from the sendmail.cf file indicates the version and vendor associated with the configuration file. # level 9 config file format V9/Berkeley The line above identifies this configuration file as corresponding with the open−source Berkeley distribution of sendmail V9. The next lines refer to certain security features: # override file safeties − setting this option compromises system security # addressing the actual file configuration problem is preferred # need to set this before any file actions are encountered in the cf file #O DontBlameSendmail=safe This version of sendmail is, by default, somewhat paranoid, judging from the previous three commented lines. By not setting DontBlameSendmail=safe, sendmail won’t accept .forward files, include files, incoming mailboxes, configuration files, class files, or hashed map files that are group− or world−writable, or that are located in a directory that is group− or world−writable. If you need to override these defaults, you can remove the comment character (#) in front of the DontBlameSendmail line. The next lines relate to LDAP maps. # default LDAP map specification # need to set this now before any LDAP maps are defined #O LDAPDefaultSpec=−h localhost With the LDAPDefaultSpec option, you can add default LDAP maps that include LDAP−specific settings. These settings apply to all LDAP maps, unless individual maps override those values. Set this option before you define any LDAP maps. sendmail local info entries The next entries in the sendmail.cf file appear under the local info heading. They enable you to enter configuration information that is specific to your local host computer. Here are the first lines you see in that section: ################## # local info # ################## Cwlocalhost # file containing names of hosts for which we receive email Fw/etc/mail/local−host−names The previous lines have similar functions. The Cwlocalhost line defines the class macro w, which contains a list of all possible hostnames given to the machine. This includes any DNS aliases, all references in /etc/hosts, and perhaps even incorrect names used by individuals with accounts on that machine (to avoid having those messages bounced). Because this could become quite an extensive list on some hosts, the Fw/etc/mail/local−host−names line defines the file class macro w, which enables these hostnames to be stored in a separate file, /etc/mail/local−host−name in this case. The next lines are used to set your TCP/IP domain name: # my official domain name # define this only if sendmail cannot automatically determine your domain #Dj$w.Foo.COM If the last of the previous lines is uncommented, the line sets the predefined macro j (the host’s canonical fully qualified domain name) to be the value of the class w (the hostname only), followed by the domain name (alternatively, the class m if it is defined). Of course, you would want to replace Foo.COM with your domain name. It is recommended that you let sendmail determine the canonical name. The next lines let you configure smart relay and other options: CP. # "Smart" relay host (may be null) DS # operators that cannot be in local usernames (i.e., network indicators) CO @ % ! # a class with just dot (for identifying canonical names) C # a class with just a left bracket (for identifying domain literals) C[[ The preceding DS line could be used to define a smart relay host. Though it is more commonly used with UUCP as a transport mechanism, this can also be useful if the machine doesn’t have a reliable connection to the entire network (perhaps it’s only on a local network). The relay accepts mail from this machine and handle delivering the mail to the appropriate recipients. The other lines define class macros that become important within the rewriting rules. The CP. and C lines define the classes P and ., each of which consists of only a period (.). The CO @ % ! line defines the class O, which lists three characters that are invalid within user names (@, %, and !). The C[[ line defines the class [, which consists of a left bracket. The next lines identify the virtual user table and the access list database: # Virtual user table (maps incoming users) Kvirtuser hash −o /etc/mail/virtusertable # Access list database (for spam stomping) Kaccess hash −o /etc/mail/access The previous Kvirtuser and Kacess lines define two key database files. The Virtual user table database (/etc/mail/virtusertable.db) is created from the hashed output of the /etc/mail/virtusertable text file. The Access list (/etc/mail/access.db) database, created from the /etc/mail/access file, lets you discard and reject e−mail from certain users to prevent spamming. See the sidebar "Forwarding E−mail and Stopping Spamming," which describes how to set up the virtual user and access list databases. Forwarding E−mail and Stopping Spamming The /etc/mail/virtusertable and /etc/mail/access files can be set up to forward e−mail and to discard e−mail from unwanted users. The virtusertable file is most commonly used on machines that receive mail for multiple domains. It enables you to redirect incoming messages. Here are some examples of mappings that could be in the virtusertable file: @township.org wilhelm@orgnet.com videotech@myotherbox.org hadji sales@verysmallcompany.com george@wehavenomoney.com The first line delivers all mail sent to a township.org to wilhelm@orgnet.com. The second line redirects mail intended for videotech@myotherbox.org to the local user account hadji. The third line redirects mail for sales@verysmallcompany.com to the remote user george@wehavenomoney.com. Similarly, the Access list database is created from /etc/mail/access. It can be used to selectively accept, reject, relay, or discard any message based on the address, hostname, domain name, or IP address contained within the header: ads@freestuff.net DISCARD junkmail.com REJECT coupons.junkmail.com OK spam.junkmail.com 550 Unsolicited bulk email will be stored and handled for a fee of $500/KB The first line in the preceding block discards (without returning any error messages) all mail from ads@freestuff.net. The second line rejects all mail from within the junkmail.com domain, returning a general delivery status notification message to the sender. However, the third line overrides the previous setting by allowing mail from coupons.junkmail.com, and the fourth line returns the specified error code to the particularly annoying spam.junkmail.com domain. The FR−o line identifies a file that can be configured to allow mail relaying. The DR and DH lines refer to where e−mail with unqualified names and local e−mail are sent: # Hosts for which relaying is permitted ($=R) FR−o /etc/mail/relay−domains # who I send unqualified names to (null means deliver locally) DR # who gets all local email traffic ($R has precedence for unqualified names) DH The first line in the preceding block declares the file class R, which is a list of hosts to which mail can be sent for relaying, stored in the file /etc/mail/relay−domains. The second and third lines can be used to define two macros, R and H, which contain the names of machines to which mail can be relayed. Add hostnames to the relay−domains file for that feature to work. Add a hostname after DR to identify the host to which mail with unqualified names is sent, and add a hostname after DH to identify the host to which all local e−mail is sent. The next lines have to do with dequoting: # dequoting map Kdequote dequote The Kdequote line declares the dequote database of class dequote. This is used to remove quotation marks from addresses within the rewriting rules. The next lines relate to how user names and domain names are exposed to the outside world: # class E: names that should be exposed as from this host, even if we masquerade # class L: names that should be delivered locally, even if we have a relay # class M: domains that should be converted to $M # class N: domains that should not be converted to $M The preceding class E line (CE root) indicates that mail from the user root should always have the appropriate full hostname and domain name, even if other directives indicate that the hostname should be masquerading as some other name. The related class L could be used to list those user names that should receive mail on the local host, even if other directives indicate that all mail should be relayed elsewhere. The class M could be used to indicate which domains should have their hostnames masqueraded (as set in the following M macro). The class N could be used to indicate hostnames that should not be masqueraded. The next lines also address masquerading: # who I masquerade as (null for no masquerading) (see also $=M) DM # my name for error messages DnMAILER−DAEMON CPREDIRECT # Configuration version number DZ8.11.4 The preceding DM line (the macro M) defines the name used in place of the machine’s real hostname. The macro n defines the user name (or alias) that is used as the sender of error messages. The CPREDIRECT line adds the text REDIRECT to the class P, which was defined several blocks earlier. This is used in conjunction with the redirect feature (enabled in the m4 configuration files), which allows aliases to be created for accounts that are no longer active. For example, if the /etc/aliases file contained the following line: jefft: jefft@newplace.com.REDIRECT any mail sent to jefft on the local machine would result in an informational message being returned to the original sender, indicating the changed address. The original mail message will not be forwarded to the address listed in the jefft example above. The DZ8.11.4 line sets the macro Z, which contains the full version information for the sendmail daemon. sendmail options The sendmail.cf file contains a long list of options that you can set for sendmail on your Red Hat Linux system. Option definitions start after the Options block. Here is an example of the beginning of the Options section: ############### # Options # ############### # strip message body to 7 bits on input? O SevenBitInput=False # 8−bit data handling # O EightBitMode=pass8 The SevenBitInput option indicates that sendmail should not clear the most significant bit from each byte of all mail messages. The EightBitMode option dictates how sendmail should handle message data that is not explicitly labeled as 8−bit. The pass8 option allows any 8−bit data to be delivered unaltered; mimefy converts any unspecified data to a MIME−encoded type; strict rejects any unlabeled 8−bit data. Note that this option has no effect on data that is specified as 8−bit. The next lines relate to alias files: # wait for alias file rebuild (default units: minutes) O AliasWait=10 # location of alias file O AliasFile=/etc/aliases Before rebuilding the aliases database, sendmail performs several checks to make sure that no other processes are attempting to do the same. The AliasWait option specifies the number of minutes that sendmail alternates between waiting and performing its checks. The AliasFile option specifies the location of the plain−text file containing mail aliases. The next lines relate to how disk space is allocated for sendmail: # minimum number of free blocks on filesystem O MinFreeBlocks=100 # maximum message size #O MaxMessageSize=1000000 The MinFreeBlocks option specifies that a message will be rejected if the acceptance of that message would cause there to be less than 100 free blocks (100K) available on the file system where messages are stored. The MaxMessageSize, if uncommented, can impose a limit on the maximum size of an incoming e−mail message (1MB in the preceding line). By default, there is no restriction on the size of a message. The next lines are for substituting characters for blank space: # substitution for space (blank) characters O BlankSub=. The BlankSub option substitutes the specified character (a . here) in place of a blank space (which is an illegal character) in an e−mail address. The next lines are for avoiding expensive mailers: # avoid connecting to "expensive" mailers on initial submission? O HoldExpensive=False If an MDA definition (explained later in this section) includes the option F=e, the mailer is classified as expensive, which simply indicates that delivering that mail may involve a slow connection or other processing delay. The HoldExpensive option allows messages handled by an expensive MDA to be queued rather than processed immediately. The preceding line disables this option. The next lines relate to checkpoint queues: # checkpoint queue runs after every N successful deliveries #O CheckpointInterval=10 When delivering messages to many addresses (as in a mailing list scenario), sendmail occasionally needs to record which recipients have already received the message and which have not. The CheckpointInterval option specifies the number of recipient addresses processed between updates of the qf file. The preceding line is commented out, but the default value is 10 anyway. The next lines relate to delivery mode: # default delivery mode O DeliveryMode=background The four possible DeliveryMode values are as follows: • background — Sendmail forks (splits off) a copy of itself and asynchronously processes the message. The default mode is background. • deferred — The message is queued and all processing, including DNS lookups and database accesses, is deferred until the queue is run. • interactive — The queue is processed synchronously, in the foreground. • queueonly — Much like deferred, but hostnames are resolved and databases are queried immediately. The next lines relate to rebuilding the alias database: # automatically rebuild the alias database? # NOTE: There is a potential for a denial of service attack if this is set. # This option is deprecated and will be removed from a future version. O AutoRebuildAliases= If no argument is specified, AutoRebuildAliases is set to true. In this case, if sendmail discovers that the modification time of the /etc/aliases file is newer than that of the /etc/aliases.db file, the Berkeley database file is rebuilt. The next lines relate to error message headers and error modes: # error message header/file #O ErrorHeader=/etc/mail/error−header # error mode #O ErrorMode=print The ErrorHeader option allows the text of a specified file to be included in all delivery status messages returned to the sender, along with any error messages from the xf file. The ErrorMode option provides five possible methods of displaying error messages to users on the local machine who encounter problems while attempting to send mail: • e — Mail an error message to the sender, but terminate successfully. • m — Mail an error message, and exit with an error code. • p — Print the error message to the user’s terminal and save the message in ~/dead.letter. This is the default. • q — Quietly ignore all delivery errors. • w — Write the error message to the user’s terminal. The next lines relate to the From lines in e−mail messages: # save Unix−style "From_" lines at top of header? #O SaveFromLine=False By default, the SaveFromLine option is disabled (False). The result is that lines within mail messages that begin with the text “From” (a special token that differentiates the end of one message from the headers of the next) will be prefaced by a > in the delivered message. The next lines relate to permissions of temporary files: # temporary file mode O TempFileMode=0600 The TempFileMode option sets the file permissions of temporary files to be readable only by the owner of the file. All other modes are highly discouraged. The next lines relate to the GECOS field: # match recipients against GECOS field? #O MatchGECOS=False The MatchGECOS option lets sendmail deliver mail to a converted form of a user’s full name, as specified in the GECOS field of the /etc/passwd file. For example, if the full name of user wharris (according to the GECOS field) is Wayne Harris, that user could receive mail as wharris@mybox.com, Wayne_Harris@mybox.com, or Wayne.Harris@mybox.com. This option is not recommended, because it could lead to ambiguities, and users could change their GECOS fields in a way that could subvert sendmail’s usual delivery mechanisms. The next lines relate to hop counts: # maximum hop count #O MaxHopCount=17 The MaxHopCount option specifies the largest number of hops (a transmission of the message from one machine to another) before a message is returned to the sender as undeliverable. The default value is 17. The next lines relate to the sendmail help file: # location of help file O HelpFile=/etc/mail/helpfile The HelpFile option lists the name of the file containing the online help text. To view this data, execute the command telnet localhost 25 and type help. Help is also available for most SMTP commands using the help command via help command name. The next lines relate to dots as terminators: # ignore dots as terminators in incoming messages? #O IgnoreDots=False The IgnoreDots option determines the behavior of sendmail when presented with a message that contains a single . on a line. With the option nonexistent, commented, or set to False, the single dot is treated as the end of the message (the behavior specified in RFC 821). If the option is set to True, the dot assumes no special significance. The next lines relate to resolver options: # name resolver options #O ResolverOptions=+AAONLY The ResolverOptions option can be used to tune the behavior of DNS lookups. Descriptions of the available flags can be found in the man page for resolver (type man resolver). The next lines relate to MIME errors: # deliver MIME−encapsulated error messages? O SendMimeErrors=True The SendMimeErrors option defines whether delivery status notification messages should be MIME−encoded or left as plain text. The next lines relate to search paths used for forwarding e−mail messages: # Forward file search path O ForwardPath=$z/.forward.$w:$z/.forward The ForwardPath option specifies the search path for an individual user’s .forward file. In the preceding line, $z represents the user’s home directory, and $w indicates the local machine’s hostname. For example, if /home/kzabon were the home directory for the user kzabon on the local machine al, sendmail would first look for the file /home/kzabon/.forward.al, followed by /home/kzabon/.forward. If neither file existed, the mail would be delivered to the incoming mailbox file /var/spool/mail/kzabon. The next lines relate to how caching is used on open connections: # open connection cache size O ConnectionCacheSize=2 # open connection cache timeout O ConnectionCacheTimeout=5m Rather than open a connection to a host, send a message, close the connection, and then open another connection to the same host, connection caching allows sendmail to send multiple mail messages to the same machine over one connection. This ConnectionCacheSize option can reduce the overhead of creating and destroying connections. The default value of 2 indicates that a maximum of two simultaneous connections can be maintained. The ConnectionCacheTimeout value specifies the maximum amount of time that a connection can be maintained. The default value is 300s, which is equivalent to 5m (five minutes). The next lines relate to the host status directory and thread deliveries: # persistent host status directory #O HostStatusDirectory=.hoststat # single thread deliveries (requires HostStatusDirectory)? #O SingleThreadDelivery=False The HostStatusDirectory option can establish a directory (relative to the queue directory /var/spool/mqueue if a full pathname isn’t specified) that stores status information for all machines with which sendmail has established a connection. This option is not set by default, because its implementation consumes resources but may not provide a substantial gain. The SingleThreadDelivery option ensures that there is always a maximum of one connection to any given machine. This, too, may not be desirable. Not only does it require the HostStatusDirectory option, it may also prevent any outgoing messages to a host if the local machine is currently processing a high volume of mail from that same machine. The next lines relate to the Errors−To header: # use Errors−To: header? O UseErrorsTo=False The UseErrorsTo option allows sendmail to utilize or ignore the “Errors−To:” header line. If set to True, any delivery errors are reported to the address specified in the header line. Otherwise, this line is ignored. The option is set to False by default because this behavior violates RFC 1123. The next lines relate to the log level: # log level O LogLevel=9 The LogLevel option sets the priority and severity of logging messages sent to the syslog facility. Values range from 0 (only severe errors are reported) to 98 (maximum debugging information is logged, along with all the more important messages). Unless you need to view copious amounts of debugging information while tracking down a mail delivery problem, the default value of 9 provides a suitable level of detail. The next lines relate to how messages are sent to the message sender: # send to me too, even in an alias expansion? #O MeToo=True The MeToo option selects sendmail’s behavior when the sender of a message is also on the mailing list’s distribution list. Unless a value of True is specified, the sender does not receive the message (based on the assumption that if the sender wrote the message, the sender doesn’t need to see it again). The next lines have to do with evaluating addresses: # verify RHS in newaliases? O CheckAliases=False If the value is set to True, the CheckAliases option evaluates addresses on the left side of the colon and guarantees a valid delivery agent for addresses on the right side. The default value is False. The next lines relate to old−style headers: # default messages to old style headers if no special punctuation? O OldStyleHeaders=True Lists of recipients were originally delimited by spaces. More recently, commas have been used because recipient names frequently contain spaces. When set to True, the OldStyleHeaders option allows comma−delimited lists, but unquoted spaces are converted to commas. If the option is set to False (the default), uncommented spaces are converted to the character specified by the BlankSub option. The next lines relate to SMTP daemon options: # SMTP daemon options # DaemonPortOptions=Name=MTA O DaemonPortOptions=Port=smtp, Addr=127.0.0.1, Name=MTA # SMTP client options #0 ClientPortOptions=Address=0.0.0.0 The DaemonPortOptions option can be used to restrict the port number and network on which sendmail will listen for incoming connections, the number of simultaneous incoming connections, and the size of the TCP/IP send and receive buffers. Note By default, the DaemonPortOption=Port=smtp line shown above restricts access to the smtp port (Port 25) and only to the local host (Addr=127.0.0.1) for mail transfer (Name=MTA). You must change or comment out the line to allow your mail server to accept mail from host computers other than the local host. The ClientPortOptions option is the same as DaemonPortOptions, except that it works for outgoing connections rather than incoming connections. The next lines relate to privacy: # privacy flags O PrivacyOptions=authwarnings,novrfy,noexpn,restrictqrun [...]... aware that the file is being downloaded from an FTP server Attributes of FTP servers That FTP was implemented on large, multiuser UNIX systems accounts for many of the design decisions that remain a part of FTP today As the most popular free version of UNIX, Linux in general (and Red Hat Linux in particular) has drawn on FTP features that have resulted from years of testing and experience gained from... an FTP server and focuses on the Washington University FTP Server software (wu−ftpd) provided with Red Hat Linux This package has been battle tested and includes particularly good tools for monitoring and protecting your FTP server It is also the FTP server software that is installed by default with Red Hat Linux Caution If you are using an FTP server only to share public files, there are minimal security... accounts to your Red Hat Linux system (that is, you know them and have given them permission for other uses besides FTP) A guest user is similar to a real user account, except that he or she has more restrictive access to the computer’s file system Procedures for setting up these different kinds of users are outlined later in this chapter Running the FTP Server When you install Red Hat Linux, your system... /etc/smrsh) Summary Installing a mail server in Red Hat Linux is the easy part; it’s the configuration that takes patience, resolve, and a fair bit of experimentation Even though it may be considerably faster and easier to utilize the m4 macros, eventually you’ll need to edit the sendmail.cf file Just hope that it’s not the rewriting rules that need editing Sooner or later, an alias definition in /etc/aliases... used to alter the priority of a message in the queue based on its precedence class or number of recipients The RetryFactor option can be used to alter the priority of a message in the queue that has already been processed but couldn’t be delivered The QueueSortOrder option, which can select the method used to determine the queue priority, can be set to host (the messages in the queue are sorted based... /bin directory contains executable commands that FTP may need (such as compress, ls, and gzip) The /etc directory contains passwd and group entries The /lib directory holds shared object libraries needed by FTP Finally, the /pub directory is available for placing the files that you want to be generally available to anonymous users Note Previous to Red Hat Linux 7, the location of the FTP home directory... equate precedence values with the possible precedence names in message headers The meaning of each precedence name is indicated in Table 19−5 The numbers by themselves aren’t significant, except in relation to other precedence names Also note that incoming mail is processed immediately (unless otherwise restricted), so these priority values apply only to messages in the queue Table 19−5: Precedence Names... these files exist For any file that begins with the word README, a message is displayed by the server that says "Please read the file README.whatever." ♦ message — This indicates that the message contained in the /welcome.msg file should be displayed when a user logs in to FTP A similar line indicates that the message file is displayed when the user enters a directory that contains such a file By default,... defines the format of the “From” header line that is used as a message separator within mailbox files The default value of $g $d prints the sender’s e−mail address, followed by two blank spaces and the local date and time at which the message was received The next lines define how to handle embedded newlines: # From: lines that have embedded newlines are unwrapped onto one line #O SingleLineFromHeader=False... file If you make changes to this file, dnl you need the sendmail−cf rpm installed and then have to generate a dnl new /etc/sendmail.cf by running the following command: dnl dnl m4 /etc/mail/sendmail.mc > /etc/sendmail.cf dnl include(`/usr/lib/sendmail−cf/m4/cf.m4') VERSIONID( `linux setup for Red Hat Linux' )dnl OSTYPE( `linux' ) define(`confDEF_USER_ID',` `8: 12'')dnl undefine(`UUCP_RELAY')dnl undefine(`BITNET_RELAY')dnl . cfhead.m4,v 8 .76 .4.16 20 01/03/06 22 :56:36 ca Exp $ ##### ##### $Id: cf.m4,v 8. 32 1999/ 02/ 07 07: 26 :14 gshapiro Exp $ ##### ##### linux setup for Red Hat Linux ##### ##### $Id: linux. m4,v 8. 11.16 .2 2000/09/ 17. blacklist_recipients.m4,v 8. 13 1999/04/ 02 02: 25:13 gs Exp $ ##### ##### $Id: accept_unresolvable_domains.m4,v 8. 10 1999/ 02/ 070 7 :26 : 07 gs Exp$ ## ##### $Id: proto.m4,v 8. 446 .2. 5 .2. 41 20 01/05 /23 21 : 32: 16 ca Exp. $Id: redirect.m4,v 8. 15 1999/ 08/ 06 01: 47: 36 gshapiro Exp $ ##### ##### $Id: always_add_domain.m4,v 8. 9 1999/ 02/ 07 07: 26 : 08 gshapiro Exp $ ##### ##### $Id: use_cw_file.m4,v 8. 9 1999/ 02/ 07 07: 26 :13