src/main/java/org/jivesoftware/smack/util/DNSUtil.java
public static List<HostAddress> resolveXMPPServerDomain(final String domain) {
        if (dnsResolver == null) {
            List<HostAddress> addresses = new ArrayList<HostAddress>(1);
            addresses.add(new HostAddress(domain, 5269));
            return addresses;
        }
        return resolveDomain(domain, 's');
    }
public static List<HostAddress> resolveXMPPServerDomain(final String domain) {
        if (dnsResolver == null) {
            List<HostAddress> addresses = new ArrayList<HostAddress>(1);
            addresses.add(new HostAddress(domain, 5269));
            return addresses;
        }
        return resolveDomain(domain, 's');
    }
Returns a list of HostAddresses under which the specified XMPP server can
be reached at for server-to-server communication. A DNS lookup for a SRV
record in the form "_xmpp-server._tcp.example.com" is attempted,
according to section 14.4 of RFC 3920. If that lookup fails, a lookup in
the older form of "_jabber._tcp.example.com" is attempted since servers
that implement an older version of the protocol may be listed using that
notation. If that lookup fails as well, it's assumed that the XMPP server
lives at the host resolved by a DNS lookup at the specified domain on the
default port of 5269.
<p>

As an example, a lookup for "example.com" may return
"im.example.com:5269".

@param domain
the domain.
@return List of HostAddress, which encompasses the hostname and port that
the XMPP server can be reached at for the specified domain.