Ldap use async MTA option

LDAP bind and connect MTA options:  (bitmask)
The  MTA option controls the use of asynchronous (as opposed  to synchronous) LDAP lookups. Asynchronous lookups avoid the need to store an entire large LDAP result in memory, which seems to cause  performance problems in some cases. This option takes a bit-encoded value. Each bit, if set, enables the use of asynchronous LDAP lookups in conjunction with a specific use of LDAP within the MTA. The following bits are defined:

Bit 0 is the least significant bit.

The default value of the  MTA option is 0, which means  that asynchronous LDAP lookups are disabled by default in the MTA.

See also:
 * LDAP bind and connect MTA options
 * ldap_group_url1 MTA Option
 * ldap_group_url2 MTA Option
 * ldap_group_dn MTA Option
 * ldap_group_dn2 MTA Option
 * Alias file named parameters
 * alias_auth_list Option
 * alias_moderator_list Option
 * alias_sasl_auth_list Option
 * alias_sasl_moderator_list Option
 * alias_cant_list Option
 * alias_sasl_cant_list Option
 * alias_originator_reply Option
 * alias_deferred_list Option
 * alias_direct_list Option
 * alias_hold_list Option
 * alias_nohold_list Option
 * alias_username_auth_list Option
 * alias_username_moderator_list Option
 * alias_username_cant_list Option
 * ldap_cant_url MTA Option
 * ldap_auth_url MTA Option
 * ldap_moderator_url MTA Option
 * ldap_jettison_url MTA Option