I am using SMACK 4.0.6. It appears to me that the exception is caused by a bug on line 53 of org.jivesoftware.smack.util.DNSUtil. There is a missing dot after "org.jivesoftware.smack.util.dns" + resolver. In my case this causes the class loader to look for org.jivesoftware.smack.util.dnsjavax.JavaxResolver, org.jivesoftware.smack.util.dnsminidns.MiniDnsResolver and
Has this been reported and is there a fixed version?