34.6.1 File Locations

The only file that sendmail knows the location of is its configuration file. [3] Options in the configuration file tell sendmail where all other files and directories are located. The options that specify file locations are summarized in Table 34.6. All file location options are of type string.

[3] Beginning with V8.6 sendmail, it also knows the location of its pid file.

File locations should be expressed as full pathnames. Use of relative names will cause the location to become relative to the queue directory or, for some options, will cause the name to be interpreted as something other than a file or directory name.

34.6.2 The Queue

Several options combine to determine your site's policy for managing the sendmail queue (see Chapter 23, The Queue). Among them is one that specifies the location of the queue directory and another that sets the permissions given to files in that directory. The list of all options that affect the queue is shown in Table 34.7.

34.6.3 Managing Aliases

In addition to knowing the location of the aliases file, some options determine how that file and its associated database files will be used. For example, there is an option that tells sendmail to automatically rebuild the database files whenever the aliases file is changed. The list of all aliases-related options is shown in Table 34.8.

34.6.4 Controlling Machine Load

Several options control the sendmail program's behavior under high-machine-load conditions. They are intended to reduce the impact of sendmail on machines that provide other services and to help protect sendmail from overburdening a machine. The list of options that determine and help to prevent high-load conditions is shown in Table 34.9.

34.6.5 Connection Caching

V8 sendmail has connection caching to improve the performance of SMTP-transported mail. In processing the queue or delivering to a long list of recipients, keeping a few SMTP connections open (in case another message is for one of those same sites) improves the speed of transfers. Caching is most useful on busy mail hub machines but can benefit any machine that sends a great deal of network mail. Table 34.10 lists the options for how connections will be cached.

The sendmail program checks its connection cache just before opening up a new connection to a host. If the cache contains an entry for that host, sendmail sends an SMTP RSET command to the host to make sure the connection is still active. If the SMTP RSET succeeds, the connection is re-used. If the SMTP RSET times out (see Section 34.8.70.18, the Timeout.rset option), or fails, or if the host was not in the cache, an new connection is made.

34.6.6 Problem Solving

The sendmail program offers four options that will help in locating and solving some mail delivery problems. You are encouraged to enable the first two shown in Table 34.11. The third is of value only if you have many delivery agents (see Chapter 30, Delivery Agents).

Other means to solve problems are described in Chapter 37, Debugging with -d, which describes the -d debugging command-line switch, and in Chapter 36, The Command Line, (specifically Section 36.4, "Processing the Command Line"), which describes the -X traffic-logging command-line switch.

34.6.7 Other Options

The sendmail program supports a vast array of options. Take the time to study all the options (described at the end of this chapter) at least enough to get a basic feeling for what they do. Then, as you gain experience with sendmail, you'll know where to look for the particular option that will meet your needs.