For safety sake, and to ensure that no email messages are ever lost,
sendmail queues all messages prior to the first
delivery attempt. The
SuperSafe option (SuperSafe) controls this behavior. When sending huge
amounts of mail to lists of subscriber recipients, however, the
safety of any single message can be less important than the overall
speed of delivery.
Although we do not recommend turning off the
SuperSafe option, you can do so when you can
tolerate the loss of messages should a mail-sending machine crash:
define(`confSAFE_QUEUE',`False') ←all versions, see later
SuperSafe option causes every message not only
to be queued, but also to be flushed to that queue and the file
synced to disk. In a situation where most email is delivered on the
first try, a benefit derived from turning off
SuperSafe is that most messages will never be
saved to disk. They will instead be delivered out of the disk cache
in memory, greatly increasing throughput.
Note that, at sites that mix subscription and internal email, simply
turning off the
SuperSafe option might not be the
best solution. While it might be acceptable to lose subscription
mail, losing internal company email probably isn’t.
An alternative to queueing or not queueing everything is to use buffered file I/O to queue portions of messages or messages over a certain size. Buffered I/O was introduced in V8.10 sendmail but was usable only with BSD-derived flavors of Unix. Beginning with V8.12 sendmail, buffered I/O ...