diff --git a/offlineimap/folder/IMAP.py b/offlineimap/folder/IMAP.py
index 464caa7..f08361b 100644
--- a/offlineimap/folder/IMAP.py
+++ b/offlineimap/folder/IMAP.py
@@ -238,7 +238,7 @@ class IMAPFolder(BaseFolder):
 
             # Then, I can do the check in the same way than Python 2
             # with string comparison:
-            if ' ' in res_data[0] or res_data[0] == '':
+            if len(res_data) > 0 and (' ' in res_data[0] or res_data[0] == ''):
                 res_data = res_data[0].split()
             # Some servers are broken.
             if 0 in res_data:
diff --git a/offlineimap/imapserver.py b/offlineimap/imapserver.py
index 49c0506..0812b3b 100644
--- a/offlineimap/imapserver.py
+++ b/offlineimap/imapserver.py
@@ -515,6 +515,10 @@ class IMAPServer:
         curThread = currentThread()
         imapobj = None
 
+        imap_debug = 0
+        if 'imap' in self.ui.debuglist:
+            imap_debug = 5
+
         if len(self.availableconnections):  # One is available.
             # Try to find one that previously belonged to this thread
             # as an optimization.  Start from the back since that's where
@@ -547,6 +551,7 @@ class IMAPServer:
                     imapobj = imaplibutil.IMAP4_Tunnel(
                         self.tunnel,
                         timeout=socket.getdefaulttimeout(),
+                        debug=imap_debug,
                         use_socket=self.proxied_socket,
                     )
                     success = True
@@ -563,6 +568,7 @@ class IMAPServer:
                         ca_certs=self.sslcacertfile,
                         cert_verify_cb=self.__verifycert,
                         ssl_version=self.sslversion,
+                        debug=imap_debug,
                         timeout=socket.getdefaulttimeout(),
                         fingerprint=self.fingerprint,
                         use_socket=self.proxied_socket,
@@ -576,6 +582,7 @@ class IMAPServer:
                         self.hostname, self.port,
                         timeout=socket.getdefaulttimeout(),
                         use_socket=self.proxied_socket,
+                        debug=imap_debug,
                         af=self.af,
                     )