Dirsync_hack MTA option
From MsgServerDocWiki
Dirsync mode control (dirsync_hack)
In dirsync mode, the dirsync_hack MTA option enables the "hack" where when a user is not found in the alias database, fall back to attempting to do an LDAP lookup on the user and plugging the user address, if found in LDAP, into the alias database. The default is 0 (false), meaning that this is not attempted. Setting this option to 1 (true) causes this LDAP-lookup-and-plug-into-LDAP "hack" to be attempted.
The dirsync_hack option affects the value of the alias_magic MTA option.
Caution: Usage of the dirsync_hack option has been DELETED. This option must not be used.
See also: MTA options, Option value syntax, Getting option changes to take effect, MTA options, listed alphabetically, MTA options, listed by functional groups, Alias and address options, alias_magic MTA option.

