Definition

Fully qualified host name of the MTA responsible for making routing decisions for users in this (and all contained) domain(s). Unspecified attribute implies all MTA's must route messages for the users/groups of this (and contained) domain(s).

When a domain is found to be non-local, the use of this attribute depends on the value of the MTA option ROUTE_TO_ROUTING_HOST:

• If the value is zero (0), which is the default setting, the attribute was checked as part of the $* rewrite rule. With a non-local domain, the $* rewrite rule fails and no further use is made of this attribute’s values. The remaining rewrite rules determine the handling of the domain.

• If the value of the option is one (1), then the first value of this attribute that the MTA receives is installed as the source route in the address. And, all addresses associated with the domain are routed to that host.

Since this attribute is multi-valued and the first value the MTA “sees” will be chosen when the option is set to 1, it might be tempting to assume that you can direct the order in which these mail hosts will be used; that is, you might assume you can do a sort of load balancing by ordering the various values of this attribute. But, LDAP does not guarantee that attribute value ordering is preserved, so the first value seen by the MTA might be any of the attribute’s values, not necessarily the first one in the LDAP entry.

You can implement load balancing with a set of MX records for each of the routing host names. Do not attempt to do it with the ordering of this attribute’s values.

LDAP_DOMAIN_AATR_ROUTING_HOSTS is the MTA option used to specify a different attribute name for this function.