barcode dll for vb.net Services, Directories, and Applications in Software

Generating UPC Code in Software Services, Directories, and Applications

confMAILER_NAME The alias used for returning messages and other automatically generated mail sent by the system. This is generally set to MAILER-DAEMON, which is typically aliased to root. So, it s possible to just set the value to root. confMAX_MESSAGE_SIZE The maximum size, in bytes, of any message that is accepted for delivery. Although large attachments are common these days, an upper limit of a few megabytes should be set, to prevent a denial of service attack. confSMTP_LOGIN_MSG Replaces the standard sendmail version banner with a local (usually nondescript) message. Can be useful in preventing would-be crackers from attempting an exploit that is specific to your version of sendmail.

The following is a sample sendmail.mc file that contains some of the parameters, features, and macros discussed in the previous sections:

OSTYPE( solaris2 ) define( confDOMAIN_NAME , cassowary.net ) define( confLOG_LEVEL , 13 ) define( confMAILER_NAME , root ) define( confMAX_MESSAGE_SIZE , 1048576 ) define( confSMTP_LOGIN_MSG , No Name Mail Server ) FEATURE( smrsh , /usr/sbin/smrsh ) FEATURE(redirect) FEATURE(always_add_domain) FEATURE(blacklist_recipients) FEATURE( access_db )

There are more extensive examples for many different configuration files supplied with the sendmail source. In particular, Eric Allman s excellent readme file should be read by anyone who is seriously contemplating extensive sendmail configuration.

Configuring sendmail (sendmail.cf)

The sendmail.cf file consists of single-line commands, which can range from rules and macros to options and headers. Some of these commands must appear only once if they specify a directive that affects the interpretation of rules (there can, however, be many rules in a sendmail.cf file). The main kinds of commands in a sendmail.cf file are

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C Specifies a class that can contain more than one item. For instance, C{MAILCLIENTS} mars venus pluto specifies an array that contains a list of mail clients (mars, venus, and pluto). D Specifies a macro. For example, DR mail.companyA.com specifies a macro named R whose contents is mail.companyA.com. E Specifies an environment variable. As a security measure, sendmail does not use environment information passed to it, preferring to use values specified in the sendmail.cf file. To set the location of a Java Virtual Machine (JVM), which may be used to support some mail-related applications, use the variable specification EJVM=/usr/local/java/bin/java. H Specifies a header, such as the Received: header. These definitions now can be very complex because of the inclusion of multipart MIME messages. M Specifies the mail-delivery agent. For instance, Mlocal, P=/bin/mail specifies that /bin/mail is the mail-delivery agent, which is usually the case under Solaris. O Specifies an option. For example, setting O SendMimeErrors=True enables the sending of MIME-encapsulated error messages. P Sets message precedence. For example, first-class mail is set with a precedence of zero (Pfirst-class=0), while junk mail is set with a precedence of 100 (Pjunk=-100). R Specifies a rule. For example, the rule R$- $@ $1 @ ${Mydomain} Rewrite address appends the FQDN defined by the macro ${Mydomain} to a username. S Indicates the start of a rule set, which can be specified either as a number (e.g., S2 for ruleset 2) or with a label (e.g., SDomainRules for the DomainRules rule set). Six kinds of system-defined rule sets are contained in the sendmail.cf file: S0 Handles basic address parsing. For example, if a user address is not specified, the error message User Address Required is returned. S1 Processes the e-mail sender s address. S2 Processes the e-mail recipient s address. S3 Performs name canonicalization and initiates the rewriting rules. For example, invalid addresses are checked (e.g., those with colons), and any angle brackets (<>) are stripped from the address. S4 Performs the final output post-rewriting, including conversion of expanded addresses like pwatters%mail@companyA.com to pwatters@mail.companyA.com. S5 The final rewriting rule set that occurs after all aliases, defined in /etc/ aliases, have been expanded.

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