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.
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.
Parameters: domainName - the String domain for which SMTP host addresses aresought. an Enumeration in which the Objects returned by next()are instances of SMTPHostAddresses.