Ldap_default_domain MTA option
Direct LDAP attribute interpretation options:
ldap_default_domain MTA option specifies the domain name that is recognized and interpreted as the default domain by the MTA. In legacy configuration, this option, if set, overrides the configutil parameter
service.defaultdomain. In Unified Configuration, this option, if set, overrides (for MTA purposes) the base level
defaultdomain option -- but it would be more normal/preferable to only set
defaultdomain so that all components of Messaging Server have a consistent choice of default domain.
In particular, in
delivery_options substitutions, the canonical domain name for the domain in which a user is located is compared against the
ldap_default_domain value. If they match, then substitutions such as
$I will not insert a domain name; that is,
ldap_default_domain is the domain name for which (in typical configurations) usernames will be left "bare" when constructing a mailbox.
ldap_default_domain also specifies the domain name that preferentially will be returned for Sieve environment "
domain" tests; if it is not set, then the MTA falls back to the
received_domain if set, or otherwise the official hostname of the L channel.