Asynchronous lookups avoid the need to store an entire large LDAP result in memory, which can cause performance problems in some cases. The MTA provides the ability to perform various types of lookups done by the MTA asynchronously.
Use of asynchronous LDAP lookups is controlled by the MTA option LDAP_USE_ASYNC. This option is 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.
Table 9–11 shows the bit and value settings for the LDAP_USE_ASYNC MTA option in the option.dat file.
Table 9–11 Settings for the LDAP_USE_ASYNC MTA Option
Bit |
Value |
Specific Use of LDAP |
---|---|---|
0 |
1 |
LDAP_GROUP_URL1 (mgrpDeliverTo) URLs |
1 |
2 |
LDAP_GROUP_URL2 (memberURL) URLs |
2 |
4 |
LDAP_GROUP_DN (UniqueMember) DNs |
3 |
8 |
auth_list, moderator_list, sasl_auth_list, and sasl_moderator_list nonpositional list parameter URLs |
4 |
16 |
cant_list, sasl_cant_list nonpositional list parameter URLs |
5 |
32 |
originator_reply nonpositional list parameter URLs |
6 |
64 |
deferred_list, direct_list, hold_list, nohold_list nonpositional list parameter URLs |
7 |
128 |
username_auth_list, username_moderator_list, username_cant_list nonpositional list parameter URLs |
8 |
256 |
alias file list URLs |
9 |
512 |
alias database list URLs |
10 |
1024 |
LDAP_CANT_URL (mgrpDisallowedBroadcaster) outer level URLs |
11 |
2048 |
LDAP_CANT_URL inner level URLs |
12 |
4096 |
LDAP_AUTH_URL (mgrpAllowedBroadcaster) outer level URLs |
13 |
8192 |
LDAP_AUTH_URL inner level URLs |
14 |
16384 |
LDAP_MODERATOR_URL (mgrpModerator) URLs |
The default value of the LDAP_USE_ASYNC MTA option is 0, which means that asynchronous LDAP lookups are disabled by default.