diff --git a/.travis.yml b/.travis.yml
index 580df32..d6ed783 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,14 +6,15 @@ python:
 install:
   - pip install -r requirements.txt
 
-matrix:  # allow Python 3 to fail until web.py is Py3-ready
-  allow_failures:
-    - python: "3.7"
+git:
+  depth: 1
 
 before_install: pip install --upgrade pip
 install: pip install flake8 pytest -r requirements.txt
 
 before_script: flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
-script:
-  - cd tests/
-  - bash main.sh
+
+# Running unittests requires a fully-working iRedMail server.
+#script:
+#  - cd tests/
+#  - bash main.sh
diff --git a/backends/bk_iredmail_ldap.py b/backends/bk_iredmail_ldap.py
index 54ad670..a0ce866 100644
--- a/backends/bk_iredmail_ldap.py
+++ b/backends/bk_iredmail_ldap.py
@@ -57,7 +57,7 @@ def __init__(self):
         try:
             # bind as vmailadmin
             self.conn.bind_s(settings.iredmail_ldap_bind_dn, settings.iredmail_ldap_bind_password)
-        except Exception, e:
+        except Exception as e:
             web.log_error('VMAILADMIN_INVALID_CREDENTIALS. Detail: %s' % repr(e))
 
     def __del__(self):
@@ -297,7 +297,7 @@ def __add_or_remove_attr_value(dn, attr, value, action, conn=None):
                 conn.modify_s(dn, [(ldap.MOD_ADD, attr, str(v))])
             except (ldap.NO_SUCH_OBJECT, ldap.TYPE_OR_VALUE_EXISTS):
                 pass
-            except Exception, e:
+            except Exception as e:
                 msg += str(e)
     elif action in ['del', 'delete', 'remove', 'disable']:
         for v in values:
@@ -305,7 +305,7 @@ def __add_or_remove_attr_value(dn, attr, value, action, conn=None):
                 conn.modify_s(dn, [(ldap.MOD_DELETE, attr, str(v))])
             except ldap.NO_SUCH_ATTRIBUTE:
                 pass
-            except Exception, e:
+            except Exception as e:
                 msg += str(e)
     else:
         return (False, 'UNKNOWN_ACTION')
@@ -344,7 +344,7 @@ def __get_primary_and_alias_domains(domain, with_primary_domain=True, conn=None)
             return (True, all_domains)
         else:
             return (False, 'INVALID_DOMAIN_NAME')
-    except Exception, e:
+    except Exception as e:
         return (False, repr(e))
 
 
@@ -411,7 +411,7 @@ def add_maillist(mail, form, conn=None):
         conn.add_s(dn_ml, ldif_ml)
         logger.info('Created: {0}.'.format(mail))
         return (True, )
-    except Exception, e:
+    except Exception as e:
         logger.error('Error while creating {0}: {1}'.format(mail, e))
         return (False, repr(e))
 
@@ -434,7 +434,7 @@ def remove_maillist(mail, conn=None):
         return (True, )
     except ldap.NO_SUCH_OBJECT:
         return (False, 'ACCOUNT_NOT_EXIST')
-    except Exception, e:
+    except Exception as e:
         logger.error("Error: {0}".format(e))
         return (False, repr(e))
 
@@ -491,7 +491,7 @@ def update_maillist(mail, form, conn=None):
             return (True, )
         except ldap.NO_SUCH_OBJECT:
             return (False, 'ACCOUNT_NOT_EXIST')
-        except Exception, e:
+        except Exception as e:
             return (False, repr(e))
     else:
         return (True, )
@@ -532,5 +532,5 @@ def get_existing_maillists(domains=None, conn=None):
             existing_lists.update(_addresses)
 
         return (True, existing_lists)
-    except Exception, e:
+    except Exception as e:
         return (False, repr(e))
diff --git a/backends/bk_iredmail_sql.py b/backends/bk_iredmail_sql.py
index d2b648b..cd3d7a5 100644
--- a/backends/bk_iredmail_sql.py
+++ b/backends/bk_iredmail_sql.py
@@ -56,7 +56,7 @@ def __init__(self):
         except (AttributeError, MySQLdb.OperationalError):
             # Reconnect if error raised: MySQL server has gone away.
             self.conn = self.__connect()
-        except Exception, e:
+        except Exception as e:
             logger.error("SQL error: {0}".format(e))
 
 
@@ -77,7 +77,7 @@ def __init__(self):
                                      user=settings.iredmail_sql_db_user,
                                      pw=settings.iredmail_sql_db_password)
             self.conn.supports_multiple_insert = True
-        except Exception, e:
+        except Exception as e:
             logger.error("SQL error: {0}".format(e))
 
 
@@ -121,7 +121,7 @@ def is_domain_exists(domain, conn=None):
 
         # Domain not exist
         return False
-    except Exception, e:
+    except Exception as e:
         # Return True as exist to not allow to create new domain/account.
         logger.error("SQL error: {0}".format(e))
         return True
@@ -159,7 +159,7 @@ def is_email_exists(mail, conn=None):
             return True
 
         return False
-    except Exception, e:
+    except Exception as e:
         logger.error("SQL error: {0}".format(e))
         return True
 
@@ -186,7 +186,7 @@ def is_maillist_exists(mail, conn=None):
             return True
 
         return False
-    except Exception, e:
+    except Exception as e:
         logger.error("SQL error: {0}".format(e))
         return True
 
@@ -305,7 +305,7 @@ def add_maillist(mail, form, conn=None):
 
         logger.info('Created: {0}.'.format(mail))
         return (True, )
-    except Exception, e:
+    except Exception as e:
         logger.error('Error while creating {0}: {1}'.format(mail, e))
         return (False, repr(e))
 
@@ -331,7 +331,7 @@ def remove_maillist(mail, conn=None):
                     where='address=$mail')
 
         return (True, )
-    except Exception, e:
+    except Exception as e:
         logger.error("SQL error: {0}".format(e))
         return (False, repr(e))
 
@@ -396,7 +396,7 @@ def update_maillist(mail, form, conn=None):
                 conn.multiple_insert('moderators', records)
 
         return (True, )
-    except Exception, e:
+    except Exception as e:
         return (False, repr(e))
 
 
@@ -432,5 +432,5 @@ def get_existing_maillists(domains=None, conn=None):
             existing_lists.add(_addr)
 
         return (True, list(existing_lists))
-    except Exception, e:
+    except Exception as e:
         return (False, repr(e))
diff --git a/backends/bk_none.py b/backends/bk_none.py
index 062a76e..d326e29 100644
--- a/backends/bk_none.py
+++ b/backends/bk_none.py
@@ -54,7 +54,7 @@ def get_existing_maillists(domains=None, *args, **kw):
         except OSError:
             # No such directory.
             pass
-        except Exception, e:
+        except Exception as e:
             return (False, repr(e))
 
         for fn in fns:
@@ -81,7 +81,7 @@ def get_existing_maillists(domains=None, *args, **kw):
         except OSError:
             # No such directory.
             pass
-        except Exception, e:
+        except Exception as e:
             return (False, repr(e))
 
     all_lists.sort()
diff --git a/libs/daemon.py b/libs/daemon.py
index c9bab23..4ef87f6 100644
--- a/libs/daemon.py
+++ b/libs/daemon.py
@@ -52,7 +52,7 @@
 
 # Default daemon parameters.
 # File mode creation mask of the daemon.
-UMASK = 0077
+UMASK = 0o077
 
 # Default working directory for the daemon.
 WORKDIR = "/"
@@ -164,7 +164,7 @@ def daemonize(noClose=False):
         if not noClose:
             _redirectFileDescriptors()
 
-    except Exception, e:
+    except Exception as e:
         raise DaemonError('Error during daemonizing: {0} [{1}]'.format(e.strerror, e.errno))
 
 
@@ -175,7 +175,7 @@ def daemonize(noClose=False):
 def _fork():
     try:
         return os.fork()
-    except OSError, e:
+    except OSError as e:
         raise DaemonError('Cannot fork: {0} [{1}]'.format(e.strerror, e.errno))
 
 
@@ -196,10 +196,10 @@ def _redirectFileDescriptors():
 
         try:
             os.close(fd)
-        except OSError, e:
+        except OSError as e:
             # File descriptor wasn't open. Ignore.
             logging.info('Error in _redirectFileDescriptors 1: ({0}, {1})'.format(e.errno, e.strerror))
-        except Exception, e:
+        except Exception as e:
             logging.info('Error in _redirectFileDescriptors 2: ({0}, {1})'.format(e.errno, e.strerror))
 
     # Redirect standard input, output and error to something safe.
diff --git a/libs/default_settings.py b/libs/default_settings.py
index 82d29ec..c33d1eb 100644
--- a/libs/default_settings.py
+++ b/libs/default_settings.py
@@ -46,7 +46,7 @@
 MLMMJ_SKEL_DIR = '/usr/share/mlmmj/text.skel'
 
 # Default file permission for created files/directories
-MLMMJ_FILE_PERMISSION = 0700
+MLMMJ_FILE_PERMISSION = 0o700
 
 #
 # Absolute path to mlmmj commands. If empty, will try /usr/bin and
diff --git a/libs/mlmmj.py b/libs/mlmmj.py
index 6e484e0..5c80f1e 100644
--- a/libs/mlmmj.py
+++ b/libs/mlmmj.py
@@ -51,7 +51,7 @@ def __remove_ml_sub_dir(mail, dirname):
         try:
             shutil.rmtree(_sub_dir)
             logger.debug("[{0}] {1}, removed sub-directory: {2}".format(web.ctx.ip, mail, _sub_dir))
-        except Exception, e:
+        except Exception as e:
             logger.error("[{0}] {1}, error while removing sub-directory: {2}".format(web.ctx.ip, mail, _sub_dir))
             return (False, repr(e))
 
@@ -65,7 +65,7 @@ def __set_file_permission(path):
     try:
         os.chown(path, _uid, _gid)
         return (True, )
-    except Exception, e:
+    except Exception as e:
         return (False, repr(e))
 
 
@@ -75,7 +75,7 @@ def __copy_dir_files(src, dest, create_dest=True):
         if not os.path.exists(dest):
             try:
                 os.makedirs(dest, mode=settings.MLMMJ_FILE_PERMISSION)
-            except Exception, e:
+            except Exception as e:
                 return (False, repr(e))
 
     for fn in os.listdir(src):
@@ -126,7 +126,7 @@ def __remove_file(path):
     if os.path.exists(path):
         try:
             os.remove(path)
-        except Exception, e:
+        except Exception as e:
             logger.error("[{0}] error while removing parameter file: {1}, {2}".format(web.ctx.ip, path, e))
             return (False, repr(e))
 
@@ -177,7 +177,7 @@ def __get_list_param_value(mail, param, is_email=False, param_file=None):
         except IOError:
             # No such file.
             pass
-        except Exception, e:
+        except Exception as e:
             logger.error('Error while getting (list) parameter value: {0} -> {1}'.format(param, e))
 
     _values.sort()
@@ -196,7 +196,7 @@ def __get_normal_param_value(mail, param, param_file=None):
     except IOError:
         # No such file.
         return ''
-    except Exception, e:
+    except Exception as e:
         logger.error("[{0}] {1}, error while getting parameter value: {2}, {3}".format(web.ctx.ip, mail, param, e))
         return ''
 
@@ -215,7 +215,7 @@ def __get_text_param_value(mail, param, param_file=None):
     except IOError:
         # No such file.
         return ''
-    except Exception, e:
+    except Exception as e:
         logger.error("[{0}] {1}, error while getting parameter value: {2}, {3}".format(web.ctx.ip, mail, param, e))
         return ''
 
@@ -323,7 +323,7 @@ def __update_boolean_param(mail,
                 _f = __get_param_file(mail=mail, param='moderated')
                 open(_f, 'a').close()
 
-        except Exception, e:
+        except Exception as e:
             logger.error("[{0}] {1}, error while updating (boolean) parameter: {2} -> {3}, {4}".format(
                 web.ctx.ip, mail, param, value, e))
             return (False, repr(e))
@@ -367,7 +367,7 @@ def __update_normal_param(mail, param, value, param_file=None, is_email=False):
             with open(param_file, 'w') as f:
                 f.write(value + '\n')
 
-        except Exception, e:
+        except Exception as e:
             logger.error("[{0}] {1}, error while updating (normal) parameter: {2} -> {3}, {4}".format(
                 web.ctx.ip, mail, param, value, e))
             return (False, repr(e))
@@ -404,7 +404,7 @@ def __update_list_param(mail, param, value, param_file=None, is_email=False):
                 f.write('\n'.join(_values) + '\n')
 
             logger.info("[{0}] {1}, updated: {2} -> {3}".format(web.ctx.ip, mail, param, ', '.join(_values)))
-        except Exception, e:
+        except Exception as e:
             logger.error("[{0}] {1}, error while updating (list) parameter: {2} -> {3}, {4}".format(
                 web.ctx.ip, mail, param, value, e))
             return (False, repr(e))
@@ -438,7 +438,7 @@ def __update_text_param(mail,
             # the characters will be a mess.
             with open(param_file, 'w') as f:
                 f.write(value + '\n')
-        except Exception, e:
+        except Exception as e:
             logger.error("[{0}] {1}, error while updating (normal) parameter: {2} -> {3}, {4}".format(
                 web.ctx.ip, mail, param, value, e))
             return (False, repr(e))
@@ -619,7 +619,7 @@ def __archive_ml(mail):
         # Create archive directory
         try:
             os.makedirs(_new_dir, mode=settings.MLMMJ_FILE_PERMISSION)
-        except Exception, e:
+        except Exception as e:
             _msg = "error while creating directory under archive directory ({0}), {1}".format(_new_dir, repr(e))
             logger.error("[{0}] {1}, {2}".format(web.ctx.ip, mail, _msg))
             return (False, _msg)
@@ -630,7 +630,7 @@ def __archive_ml(mail):
 
             # Return new directory path
             return (True, _new_dir)
-        except Exception, e:
+        except Exception as e:
             logger.error("[{0}] {1}, error while archiving: {2} ({3} -> {4})".format(web.ctx.ip, mail, e, _dir, _new_dir))
             return (False, repr(e))
 
@@ -668,7 +668,7 @@ def __remove_lines_in_file(path, lines):
                 return qr
 
         return (True, )
-    except Exception, e:
+    except Exception as e:
         return (False, repr(e))
 
 
@@ -699,7 +699,7 @@ def __add_lines_in_file(f, lines):
             nf.write(''.join(file_lines))
 
         return (True, )
-    except Exception, e:
+    except Exception as e:
         return (False, repr(e))
 
 
@@ -757,7 +757,7 @@ def __add_subscribers_with_confirm(mail,
             subprocess.Popen(_new_cmd, stdout=subprocess.PIPE)
 
             logger.debug("[{0}] {1}, queued confirm mail for {2}.".format(web.ctx.ip, mail, addr))
-        except Exception, e:
+        except Exception as e:
             logger.error("[{0}] {1}, error while subscribing {2}: {3}".format(web.ctx.ip, mail, addr, e))
             _error[addr] = repr(e)
 
@@ -893,7 +893,7 @@ def create_ml(mail, **kwargs):
     if not os.path.exists(_ml_dir):
         try:
             os.makedirs(_ml_dir, mode=settings.MLMMJ_FILE_PERMISSION)
-        except Exception, e:
+        except Exception as e:
             _msg = "error while creating base directory ({0}), {1}".format(_ml_dir, repr(e))
             logger.error("[{0}] {1}, {2}".format(web.ctx.ip, mail, _msg))
             return (False, _msg)
@@ -904,7 +904,7 @@ def create_ml(mail, **kwargs):
         if not os.path.exists(_sub_dir):
             try:
                 os.makedirs(_sub_dir, mode=settings.MLMMJ_FILE_PERMISSION)
-            except Exception, e:
+            except Exception as e:
                 _msg = "error while creating sub-directory ({0}), {1}".format(_sub_dir, repr(e))
                 logger.error("[{0}] {1}, {2}".format(web.ctx.ip, mail, _msg))
                 return (False, _msg)
@@ -955,7 +955,7 @@ def delete_ml(mail, archive=True):
             try:
                 shutil.rmtree(_ml_dir)
                 logger.info("[{0}] {1}, removed without archiving.".format(web.ctx.ip, mail))
-            except Exception, e:
+            except Exception as e:
                 return (False, repr(e))
     else:
         logger.info("[{0}] {1}, removed (no data on file system).".format(web.ctx.ip, mail))
@@ -1053,7 +1053,7 @@ def remove_all_subscribers(mail):
                 qr = __remove_file(path=_path)
                 if not qr[0]:
                     return qr
-    except Exception, e:
+    except Exception as e:
         return (False, repr(e))
 
     return (True, )
diff --git a/mlmmjadmin.py b/mlmmjadmin.py
index 95b29aa..d9b7f01 100644
--- a/mlmmjadmin.py
+++ b/mlmmjadmin.py
@@ -26,7 +26,7 @@
         sys.exit("ERROR: directory doesn't exist or incorrect permission "
                  "(check parent directories also): {0}.".format(_dir))
 
-os.umask(0077)
+os.umask(0o077)
 
 # Get uid/gid of daemon user.
 uid = pwd.getpwnam(settings.run_as_user).pw_uid
diff --git a/tests/__init__.py b/tests/__init__.py
index 443692e..de458d3 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1,3 +1,4 @@
+from __future__ import print_function
 import requests
 import settings
 
@@ -32,4 +33,4 @@ def delete(url, data=None):
 
 
 def debug(*msg):
-    print '[DEBUG]', msg
+    print('[DEBUG]', msg)
diff --git a/tools/maillist_admin.py b/tools/maillist_admin.py
index 5fd6093..76aee1b 100644
--- a/tools/maillist_admin.py
+++ b/tools/maillist_admin.py
@@ -1,3 +1,4 @@
+from __future__ import print_function
 # TODO list all mailing list accounts
 #   - if `backend` is `bk_none`, list all accounts under mlmmj spool directory.
 #   - if `backend` is not `bk_none`, query from backend.
@@ -70,7 +71,7 @@
 """
 
 if len(sys.argv) < 3:
-    print usage
+    print(usage)
     sys.exit()
 
 # Base url of API interface
@@ -94,8 +95,8 @@
                   'has_subscriber',
                   'subscribers', 'subscribed',
                   'add_subscribers', 'remove_subscribers']:
-    print '<ERROR> Invalid action: {0}. Usage:'.format(action)
-    print usage
+    print('<ERROR> Invalid action: {0}. Usage:'.format(action))
+    print(usage)
     sys.exit()
 
 mail = sys.argv[2]
@@ -122,44 +123,44 @@
             if k in ['footer_text', 'footer_html', 'name', 'subject_prefix']:
                 v = v.encode('utf-8')
 
-            print '{0}={1}'.format(k, v)
+            print('{0}={1}'.format(k, v))
     else:
-        print "Error: {0}".format(_json['_msg'])
+        print("Error: {0}".format(_json['_msg']))
 
 elif action == 'create':
     if run_backend_cli:
         # Create account in backend
         qr = backend.add_maillist(mail=mail, form=arg_kvs)
         if not qr[0]:
-            print "Error while interactive with backend:", qr[1]
+            print("Error while interactive with backend:", qr[1])
             sys.exit()
 
     r = requests.post(api_url, data=arg_kvs, headers=api_headers, verify=verify_ssl)
     _json = r.json()
     if _json['_success']:
-        print "Created."
+        print("Created.")
     else:
-        print "Error: {0}".format(_json['_msg'])
+        print("Error: {0}".format(_json['_msg']))
 
 elif action == 'update':
     if run_backend_cli:
         qr = backend.update_maillist(mail=mail, form=arg_kvs)
         if not qr[0]:
-            print "Error while interactive with backend:", qr[1]
+            print("Error while interactive with backend:", qr[1])
             sys.exit()
 
     r = requests.put(api_url, data=arg_kvs, headers=api_headers, verify=verify_ssl)
     _json = r.json()
     if _json['_success']:
-        print "Updated."
+        print("Updated.")
     else:
-        print "Error: {0}".format(_json['_msg'])
+        print("Error: {0}".format(_json['_msg']))
 
 elif action == 'delete':
     if run_backend_cli:
         qr = backend.remove_maillist(mail=mail)
         if not qr[0]:
-            print "Error while interactive with backend:", qr[1]
+            print("Error while interactive with backend:", qr[1])
             sys.exit()
 
     api_url = api_url + '?' + urlencode(arg_kvs)
@@ -167,11 +168,11 @@
     _json = r.json()
     if _json['_success']:
         if arg_kvs.get('archive') in ['yes', None]:
-            print "Removed {0} (archived).".format(mail)
+            print("Removed {0} (archived).".format(mail))
         else:
-            print "Removed {0} (without archive).".format(mail)
+            print("Removed {0} (without archive).".format(mail))
     else:
-        print "Error: {0}".format(_json['_msg'])
+        print("Error: {0}".format(_json['_msg']))
 
 elif action == 'has_subscriber':
     _subscriber = args[0]
@@ -179,12 +180,12 @@
     r = requests.get(url, headers=api_headers, verify=verify_ssl)
     _json = r.json()
     if _json['_success']:
-        print '[YES] Mailing list <{0}> has subscriber <{1}>.'.format(mail, _subscriber)
+        print('[YES] Mailing list <{0}> has subscriber <{1}>.'.format(mail, _subscriber))
     else:
         if '_msg' in _json:
-            print "Error: {0}".format(_json['_msg'])
+            print("Error: {0}".format(_json['_msg']))
         else:
-            print '[NO] Mailing list <{0}> does NOT have subscriber <{1}>.'.format(mail, _subscriber)
+            print('[NO] Mailing list <{0}> does NOT have subscriber <{1}>.'.format(mail, _subscriber))
 
 elif action == 'subscribers':
     url = api_url + '/subscribers'
@@ -192,9 +193,9 @@
     _json = r.json()
     if _json['_success']:
         for i in _json['_data']:
-            print i['mail'], '(%s)' % i['subscription']
+            print(i['mail'], '(%s)' % i['subscription'])
     else:
-        print "Error: {0}".format(_json['_msg'])
+        print("Error: {0}".format(_json['_msg']))
 
 elif action == 'subscribed':
     url = api_subscriber_url + '/subscribed' + '?' + 'query_all_lists=yes'
@@ -202,38 +203,38 @@
     _json = r.json()
     if _json['_success']:
         for i in _json['_data']:
-            print i['mail'], '(%s)' % i['subscription']
+            print(i['mail'], '(%s)' % i['subscription'])
     else:
-        print "Error: {0}".format(_json['_msg'])
+        print("Error: {0}".format(_json['_msg']))
 
 elif action == 'add_subscribers':
     url = api_url + '/subscribers'
 
     _subscribers = set([str(i).lower() for i in args if is_email(i)])
     if not _subscribers:
-        print "Error: No subscribers given."
+        print("Error: No subscribers given.")
         sys.exit()
 
     arg_kvs['add_subscribers'] = ','.join(_subscribers)
     r = requests.post(url, data=arg_kvs, headers=api_headers, verify=verify_ssl)
     _json = r.json()
     if _json['_success']:
-        print "Added."
+        print("Added.")
     else:
-        print "Error: {0}".format(_json['_msg'])
+        print("Error: {0}".format(_json['_msg']))
 
 elif action == 'remove_subscribers':
     url = api_url + '/subscribers'
 
     _subscribers = set([str(i).lower() for i in args if is_email(i)])
     if not _subscribers:
-        print "Error: No subscribers given."
+        print("Error: No subscribers given.")
         sys.exit()
 
     arg_kvs['remove_subscribers'] = ','.join(_subscribers)
     r = requests.post(url, data=arg_kvs, headers=api_headers, verify=verify_ssl)
     _json = r.json()
     if _json['_success']:
-        print "Removed."
+        print("Removed.")
     else:
-        print "Error: {0}".format(_json['_msg'])
+        print("Error: {0}".format(_json['_msg']))