The Define Class Command

Z Version number

20.2.1.1.2 The Define Class Command

Two commands, C and F, define sendmail classes. A class is an array of values. They are used when multiple values are handled in the same way; for example, multiple names for the local host, or a list of uucp names. Classes allow sendmail to compare against a list of values, instead of multiple comparisons against single values. Special pattern matching symbols are introduced for this purpose: the = symbol matches any value in a class, and the ~ symbol matches any value not in a class. Classes have single character names, and user−created classes use uppercase letters for names. Class values can be defined on a single line, on multiple lines, or loaded from a file. The C command is used to assign the class from a single or multiple lines, for example: CV host1 host2 host3 or CV host1 host2 CV host3 Each new line with values in the class definition is appended to previously defined class values. The F command is used to load the class values from a file, for example: Fw etcsendmail.cw will define the class w as the contents of the file etcsendmail.cw A few class definitions may need to be modified in the sendmail configuration file. These are classes related to the alias host names, to special domains for mail routing, or some other site−dependent data. Similarly as with macros, some of the letters are used as usual names for specific classes; they are presented in the following table: Class Description B Domains that are candidates for best MX lookup E Addresses that should not seem to come from macro M F Hosts to forward for G Domains that should be looked up in generic table L Addresses that should not be forwarded to macro R M Domains that should be mapped to macro M O Operators that indicate network operations cannot be in local names P Top level pseudo−domains: BITNET, DECNET, FAX, UUCP, etc. 474 U My UUCP name if I have a UUCP connection V UUCP hosts connected to relay macro V W UUCP hosts connected to relay macro W X UUCP hosts connected to relay macro X Y Locally connected smart UUCP hosts Z Locally connected domain−ized UUCP hosts . The class containing only a dot [ The class containing only a left bracketv The configuration file continues with the Version number. −−−−−−−−−−−−−−−−−−−−−−−− etcsendmail.cf continued −−−−−−−−−−−−−−−−−−−−−−− Version number of configuration file DVSMI−4.1 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−− to be continued −−−−−−−−−−−−−−−−−−−−−−−−−−−− The version number is the macro V, and is defined as any other macro. It usually does not require modification, but it can be a good idea to keep track of the changes made to the sendmail configuration. The version number is the place to do it. Each time the configuration is changed, the version number can be modified. Afterward, the Standard macros sometimes also known as Special macros are specified: −−−−−−−−−−−−−−−−−−−−−−−−− etcsendmail.cf continued −−−−−−−−−−−−−−−−−−−−−−−−−−−− Standard macros name used for error messages DnMailer−Daemon UNIX header format DlFrom g d delimiter operator characters Do.: = [] format of a total name Dqg?x x. SMTP login message Dej Sendmail vV ready at b −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− to be continued −−−−−−−−−−−−−−−−−−−−−−−− The Standard special macro section includes some special macros used by sendmail. For example, the name that sendmail uses to identify itself when it returns error messages, or the message that sendmail displays during an SMTP login. All macros are defined in the usual way. There is no need for any modification of this section. The Options section follows: −−−−−−−−−−−−−−−−−−−−−−− etcsendmail.cf continued −−−−−−−−−−−−−−−−−−−−−−− Options Remote mode − send through server if mailbox directory is mounted OR location of alias file OAetcaliases default delivery mode deliver in background Odbackground rebuild the alias file automagically OD temporary file mode −− 0600 for secure mail, 0644 for permissive 475 The Options section specifies all of the implemented sendmail options. A leading uppercase letter O identifies each option entry; the second letter is the option name. Occasionally, some of the options can be modified if an already defined or default option does not correspond to the real situation. When options define pathnames for needed files and directories, it is highly recommended to keep their standard locations. Besides the options defined for this specific configuration, other options are also available: Option Meaning aN Wait N min. for :, than rebuild the alias file Bc Define the blank substitution character c Queue mail for an expensive mailer di Deliver interactively dq Deliver during the next queue run ee Mail error messages and return 0 status em Mail back error messages ep Print error messages eq Return exit status; no error messages ew Write back error messages f Retain UNIX−style From lines I Use the BIND DNS to resolve host names i Ignore dots in incoming messages Mxval Set macro x to val m Send to me, too Nnet Define the name of the home network as net qn Define factor n used to decide when to queue jobs v Run in verbose mode 476 Refuse SMTP connections if load average exceeds l xl Queue messages if load average exceeds l Y Deliver each queued job in separate job yn Lower priority of a job by n for each recipient v Zn Decrease a jobs priority by n each time it is run zn Factor used with precedence to determine message priority An option could be a string, an integer, a Boolean, or a time interval. There are no user created options; the meaning of each option is hard−coded within the sendmail program. For options missing from the configuration file, the default values are supposed. The configuration continues with the sections: Message precedences and Trusted users. −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− etcsendmail.cf continued −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Message precedences Pfirst−class=0 Pspecial−delivery=100 Pjunk=–100 Trusted users T root daemon uucp −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− to be continued −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Message precedences Assigns priority to messages entering its queue it is known as message precedence; the higher the precedence number, the greater the precedence of the message the default is 0. There is no need to modify this section. • Trusted users Defines a list of users who are trusted to override the sender address using the mailer flag −f; could be a security problem, so it is better not to modify it. • The Headers section defines the format of headers that sendmail inserts into e−mail. −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− etcsendmail.cf continued −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Format of headers H?P?Return−Path: g HReceived: ?sfrom s .by j vV id i; b H?D?Resent−Date: a H?D?Date: a H?F?Resent−From: q H?F?From: q H?x?Full−Name: x HSubject: H?M?Resent−Message−Id: t.ij H?M?Message−Id: t.ij HErrors−To: −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− to be continued −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Macros defined within the headers are expanded before the header is inserted; it is unlikely to need to change the headers. For a better understanding of the headers entries, reread the paragraph on how the macros are defined. The remaining sendmail configuration lines are related to Rulesets and Rewrite Rules. This is the section that defines sendmail parsing algorithms and decision−making mechanisms. This is the most important part of the configuration file. We will return to this section later. 477 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− etcsendmail.cf continued −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Local and Program Mailer specification mandatory Mlocal, P=binmail, F=rlsDFMmnP, S=10, R=20, A=mail −d u Mprog, P=binsh, F=lsDFMeuP, S=10, R=20, A=sh −c u Ethernet Mailer specification Messages processed by this configuration are assumed to remain in the same domain. This really has nothing particular to do with Ethernet − the name is historical. Mether, P=[TCP], F=msDFMuCX, S=11, R=21, A=TCP h UUCP Mailer specification Muucp, P=usrbinuux, F=msDFMhuU, S=13, R=23, A=uux − −r −af hrmail u −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− to be continued −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Two mailers, local and prog, are mandatory for every sendmail configuration file. In this case these are the program binmail and Bourne shell binsh. Two other defined mailers are: ether for sendmail communication through the network specified by [TCP], and uucp program usrbinuux for UUCP delivery via phone line.

20.2.2 Rulesets and Rewrite Rules