At times, such as when calling /bin/mail to deliver local mail, sendmail holds an entire message internally while waiting for that delivery to complete. Clearly, this runs the risk that the message will be lost if the system crashes at the wrong time.

As a safeguard against such rare catastrophes, the SuperSafe option can be used to force sendmail to queue every message and to sync(2) the queued files to disk for maximum safety. The queued copy is left in place until sendmail is sure that delivery was successful. We strongly recommend that this option always be declared as true.

The forms of the SuperSafe option are as follows:

O SuperSafe=character                configuration file (V8.12 and later) 
-OSuperSafe=character                command line (V8.12 and later) 
define(`confSAFE_QUEUE',`character') mc configuration (V8.12 and later) 
O SuperSafe=bool                     configuration file (V8.7 and later) 
-OSuperSafe=bool                     command line (V8.7 and later) 
define(`confSAFE_QUEUE',`bool')      mc configuration (V8.7 and later) 
Osbool                               configuration file (deprecated) 
-osbool                              command line (deprecated) 

The argument, prior to V8.12, was of type Boolean. The argument, with V8.12 and later, is of type Character. If the argument is missing, the default value is true (everything is queued). The default for the mc configuration technique is also true. If the entire SuperSafe option is missing, the default for V8.11 and earlier becomes false (no special queuing behavior), but for V8.12 and later it becomes true (everything is queued).

Beginning with V8.12, a third alternative to true or false was introduced that is useful with sendmail's interactive delivery mode, and is called i for interactive. For example:

define(`confDELIVERY_MODE',`interactive')
define(`confSAFE_QUEUE',   `interactive') V8.12 and later

This interactive setting for the SuperSafe option causes sendmail to skip unneeded secondary synchronization calls.

At high-volume sites that perhaps send subscription email, there can be benefit (and increased risk) to turning off this SuperSafe option (see also Section 6.4):

define(`confSAFE_QUEUE',   `false') strongly discouraged

The SuperSafe option is safe. Even if it is specified from the command line, sendmail retains its special privileges.