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package org.apache.james.services;

import java.util.Collection;
import java.util.Iterator;

/**
 * Provides abstraction for DNS resolutions. The interface is Mail specific.
 * It may be a good idea to make the interface more generic or expose 
 * commonly needed DNS methods.
 *
 */
public interface DNSServer {

    /**
     * The component role used by components implementing this service
     */
    String ROLE = "org.apache.james.services.DNSServer";

    /**
     * <p>Get a priority-sorted collection of DNS MX records for a given hostname</p>
     *
     * <p>TODO: Change this to a list, as not all collections are sortable</p>
     *
     * @param hostname the hostname to check
     * @return collection of strings representing MX record values. 
     */
    Collection findMXRecords(String hostname);


    /**
     * Performs DNS lookups as needed to find servers which should or might
     * support SMTP.  Returns one SMTPHostAddresses for each such host
     * discovered by DNS.  If no host is found for domainName, the Iterator
     * returned will be empty and the first call to hasNext() will return
     * false.
     * @param domainName the String domain for which SMTP host addresses are
     * sought.
     * @return an Enumeration in which the Objects returned by next()
     * are instances of SMTPHostAddresses.
     */
    Iterator getSMTPHostAddresses(String domainName);
    
}