Chapter 6. Tune Performance

When sendmail is installed with near-default settings, it provides excellent email services for most machines. But when installed to service high loads, high volumes, or high rates, special tuning becomes a requirement.

What’s New with V8.13

There are a few new items in V8.13 that affect performance tuning. They are described in other chapters but referenced here. In this chapter, we augment some of the knowledge imparted in the third edition of the sendmail book.

  • The RequiresDirfsync option (Section 24.1.12 [V8.13]) turns off the REQUIRES_DIR_FSYNC (3.4.47[3ed]) compile-time macro’s setting at runtime. Turning off directory fsyncs increases performance—but at (possibly) increased risk.

  • The existing SuperSafe option (24.9.107[3ed]) now accepts a new PostMilter setting that delays fsync( )ing the df file until after all Milters have reviewed the message. This improves performance when a great deal of email is rejected by Milters that review the message body.

  • The Timeout.queuereturn.dsn (Section 24.1.15[V8.13]) and Timeout.queuewarn.dsn (Section 24.1.16 [V8.13]) options have been added. Use them to lower bounce timeouts, and thereby to create less congested queues and increase performance.

  • Some sites have developed delivery agents that receive messages using SMTP over standard input/output. Such delivery agents use the P=[LPC] equate (20.5.11[3ed]) to achieve this effect. Beginning with V8.13, sendmail enables connection caching (24.7.5[3ed]) for such ...

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