A <Multi> element is a sub-element of the <Vrfy> element. It contains any number of <LDAP>, <RcptTo>, <Postfix>, <Communigate>, and <DataBase> sub-verifiers. When a request to verify an email address is received by a Multi verifier, it queries each of its sub-verifiers in their defined order. Use a Multi verifier whenever you have one or more domains serviced by more than one server.
For example, a school might use a student-administered LDAP server to handle all the student email addresses. There is a faculty LDAP server to handle email addresses for the employees. They both require different credentials to bind to each server, and they each use a different list of BaseDNs to search. Yet, when a request to verify an email address comes in, it always contains "@school.edu". You need a single verifier to be mapped to the school.edu domain that searches each of the subordinate verifiers in turn. Multi verifiers do this.
To create a Multi verifier, wrap the sub-verifiers inside of <Multi> ... </Multi> tags in a single verifier. The <InterDiscTime> and <InterEnumTime> elements are only allowed as child elements of a Multi verifier, no other verifier type or sub-verifier can contain these elements.
The following elements can be used both as children of a sub-verifier and also as children of the <Multi> verifier itself: <Timeout>, <BackendMax>, and<BackendIdleTime>.
These elements are inheritable. This means that if a Multi verifier specifies a value for one of these elements, then all sub-verifiers that do not also specify a value (called overriding the inheritance) will inherit the value of the parent <Multi> element. In this way you can set, for example, a <Timeout> used by all the sub-verifiers in the <Multi> using only a single <Timeout> element as a child of the <Multi> element itself.
The behavior of the <InterEnumTime> element is different in Multi verifiers. Without this element, it is assumed that all the sub-verifiers have an <InterEnumTime> of 0 (zero). That is, enumeration is disabled by default on all the sub-verifiers. Because no sub-verifier is allowed to have the <InterEnumTime> element, the only way to get enumeration of sub-verifiers is to enumerate all sub-verifiers.
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