diff --git base/univention-lib/python/umc.py base/univention-lib/python/umc.py
index c9e83aba04..cd022ea230 100644
--- base/univention-lib/python/umc.py
+++ base/univention-lib/python/umc.py
@@ -41,13 +41,29 @@ connections to remote |UMC| servers
 import ssl
 import json
 import locale
-from Cookie import SimpleCookie
-from httplib import HTTPSConnection, HTTPException
 
-from univention.config_registry import ConfigRegistry
-ucr = ConfigRegistry()
-ucr.load()
+import six
 
+if six.PY3:
+	from http.cookies import SimpleCookie
+	from http.client import HTTPSConnection, HTTPException
+else:
+	from Cookie import SimpleCookie
+	from httplib import HTTPSConnection, HTTPException
+
+def _get_ucr():
+	from univention.config_registry import ConfigRegistry
+	ucr = ConfigRegistry()
+	ucr.load()
+	return ucr
+
+def _get_useragent():
+	ucr = _get_ucr()
+	return 'UCS/%s (univention.lib.umc/%s-errata%s)' % (ucr.get('version/version', '0.0'), ucr.get('version/patchlevel', '0'), ucr.get('version/erratalevel', '0')),
+
+def _get_fqdn():
+	ucr = _get_ucr()
+	return '%s.%s' % (ucr.get('hostname'), ucr.get('domainname'))
 
 class _HTTPType(type):
 	"""
@@ -340,16 +356,16 @@ class Client(object):
 
 	ConnectionType = HTTPSConnection
 
-	def __init__(self, hostname=None, username=None, password=None, language=None, timeout=None, automatic_reauthentication=False):
+	def __init__(self, hostname=None, username=None, password=None, language=None, timeout=None, automatic_reauthentication=False, useragent=None):
 		# type: (Optional[str], Optional[str], Optional[str], Optional[str], Optional[float], bool) -> None
-		self.hostname = hostname or '%s.%s' % (ucr.get('hostname'), ucr.get('domainname'))
+		self.hostname = hostname or _get_fqdn()
 		self._language = language or locale.getdefaultlocale()[0] or ''
 		self._headers = {
 			'Content-Type': 'application/json; charset=UTF-8',
 			'Accept': 'application/json; q=1, text/html; q=0.5; */*; q=0.1',
 			'Accept-Language': self._language.replace('_', '-'),
 			'X-Requested-With': 'XMLHttpRequest',
-			'User-Agent': 'UCS/%s (univention.lib.umc/%s-errata%s)' % (ucr.get('version/version', '0.0'), ucr.get('version/patchlevel', '0'), ucr.get('version/erratalevel', '0')),
+			'User-Agent': useragent or _get_useragent()
 		}
 		self._base_uri = '/univention/'
 		self._timeout = timeout
@@ -411,7 +427,7 @@ class Client(object):
 
 		:raises ConnectionError: if :file:`/etc/machine.secret` cannot be read.
 		"""
-		username = '%s$' % ucr.get('hostname')
+		username = '%s$' % _get_ucr().get('hostname')
 		try:
 			with open('/etc/machine.secret') as machine_file:
 				password = machine_file.readline().strip()
@@ -530,7 +546,7 @@ class Client(object):
 		:raises ConnectionError: if the request cannot be send.
 		:raises HTTPError: if an |UMC| error occurs.
 		"""
-		cookie = '; '.join(['='.join(x) for x in self.cookies.iteritems()])
+		cookie = '; '.join(['='.join(x) for x in self.cookies.items()])
 		request.headers = dict(self._headers, Cookie=cookie, **request.headers)
 		if 'UMCSessionId' in self.cookies:
 			request.headers['X-XSRF-Protection'] = self.cookies['UMCSessionId']