Beginning with V8.10 sendmail, it was discovered that autorebuilding the aliases database held the potential for a denial-of-service attack. If a user could kill sendmail during a rebuild, the aliases database could be left in an incomplete state, resulting in possible lost and misdirected email. As a consequence, this AutoRebuildAliases option is deprecated. Although it is present in V8.10 and V8.11, you should not use it. This option has been eliminated from V8.12.

Prior to V8.10 sendmail, the need to autorebuild the aliases database was determined by comparing the modification time of the aliases source file, as defined by the AliasFile option (AliasFile), to the modification time of the corresponding aliases.pag and aliases.dir, or aliases.db, database files. If the source file was newer and if this AutoRebuildAliases option was set, sendmail attempted to rebuild the aliases database. If this option was not set, sendmail printed the following warning and used the information in the old database:

Warning: alias database fname out of date

Here, fname is the name of the source file. If you wish to set this to AutoRebuildAliases, despite the risk, be sure that the AliasWait option (AliasFile) is also declared and given a nonzero time argument. (Note that file locking, to prevent simultaneous rebuilds, is described under the AliasWait option.)

The forms of this AutoRebuildAliases option are as follows:

O AutoRebuildAliases=bool      configuration file (V8.7 to V8.11) 
-OAutoRebuildAliases=bool      command line (V8.7 to V8.11) 
define(`confAUTO_REBUILD',bool)    mc configuration (V8.7 to V8.11) 
ODbool                         configuration file (V8.11 and earlier) 
-oDbool                        command line (V8.11 and earlier) 

With no argument, AutoRebuildAliases is set to true (the aliases database is automatically rebuilt). If the entire AutoRebuildAliases option is missing, it defaults to false (no automatic rebuilds).

IDA sendmail uses fcntl(3) to prevent simultaneous rebuilds. Ancient versions of sendmail used flock(3). V8 sendmail uses either fcntl(3) or flock(3), depending on how it was compiled.

The AutoRebuildAliases option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.