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.
To understand what we mean by high in this context, consider some
typical email sites on the Internet that have good delivery rates
despite extremely high loads. Some can deliver
email envelopes at rates exceeding 1 million envelopes per hour. Some
can accept email to mailboxes for hundreds of thousands of users.
Clearly, such volumes are well beyond the requirements of the average
In this chapter we reveal only some of the techniques used by large
sites. A full treatise on high-volume mail-handling would require a
book of its own.