The solution was to make the Digester
namespace aware and to make the rule matching ignore the namespace:
public GmailContactsDigester() {
digester = new Digester();
digester.setRuleNamespaceURI(null);
digester.setNamespaceAware(true);
digester.addObjectCreate("feed", ArrayList.class);
digester.addObjectCreate("feed/entry", GoogleContact.class);
digester.addBeanPropertySetter("feed/entry/name/givenName");
digester.addBeanPropertySetter("feed/entry/name/familyName");
digester.addRule("feed/entry/email/", new SetPropertiesRule("address", "email"));
digester.addSetNext("feed/entry", "add");
}