According to https://github.com/martinrusev/imbox/issues/68 the

software was altered, in order to use the systems SSL-Context as
default.

It allows to toggle the use of the SSL-Default Context. It does not
allow to use a custom context.

 Considerations:
 * If No SSL-Validation should be done, the ImboxClass should be adapted, in
   order to achieve configuration of the ssl-context. This commit does not
   contain this alteration.

 Other Changes:
 * Reformatted long lines

imbox/imap.py

@@ -1,25 +1,34 @@
 from imaplib import IMAP4, IMAP4_SSL
 
 import logging
+import ssl as pythonssllib
+
 logger = logging.getLogger(__name__)
 
+
 class ImapTransport(object):
 
-    def __init__(self, hostname, port=None, ssl=False):
+    def __init__(self, hostname, port=None, ssl=True, usesslcontext=True):
         self.hostname = hostname
         self.port = port
 
         if ssl:
-            self.transport = IMAP4_SSL
+            if usesslcontext = True:
+                context = pythonssllib.create_default_context()
+            else:
+                context = None
+
             if not self.port:
                 self.port = 993
+            self.server = self.IMAP4_SSL(self.hostname, self.port,
+                                         ssl_context=context)
         else:
-            self.transport = IMAP4
             if not self.port:
                 self.port = 143
 
-        self.server = self.transport(self.hostname, self.port)
-        logger.debug("Created IMAP4 transport for {host}:{port}".format(host=self.hostname, port=self.port))
+        self.server = self.IMAP4(self.hostname, self.port)
+        logger.debug("Created IMAP4 transport for {host}:{port}"
+                     .format(host=self.hostname, port=self.port))
 
     def list_folders(self):
         logger.debug("List all folders in mailbox")
@@ -28,5 +37,6 @@ class ImapTransport(object):
     def connect(self, username, password):
         self.server.login(username, password)
         self.server.select()
-        logger.debug("Logged into server {} and selected mailbox 'INBOX'".format(self.hostname))
+        logger.debug("Logged into server {} and selected mailbox 'INBOX'"
+                     .format(self.hostname))
         return self.server