Index: twisted/mail/imap4.py
===================================================================
--- twisted/mail/imap4.py	(revision 26969)
+++ twisted/mail/imap4.py	(working copy)
@@ -333,7 +333,7 @@
 
 
 class Command:
-    _1_RESPONSES = ('CAPABILITY', 'FLAGS', 'LIST', 'LSUB', 'STATUS', 'SEARCH', 'NAMESPACE')
+    _1_RESPONSES = ('CAPABILITY', 'FLAGS', 'LIST', 'LSUB', 'STATUS', 'SEARCH', 'NAMESPACE', 'BYE')
     _2_RESPONSES = ('EXISTS', 'EXPUNGE', 'FETCH', 'RECENT')
     _OK_RESPONSES = ('UIDVALIDITY', 'UNSEEN', 'READ-WRITE', 'READ-ONLY', 'UIDNEXT', 'PERMANENTFLAGS')
     defer = None
@@ -4159,7 +4159,7 @@
         return "PLAIN"
 
     def challengeResponse(self, secret, chal):
-        return '%s\0%s\0' % (self.user, secret)
+        return '\0%s\0%s' % (self.user, secret)
 
 
 class MailboxException(IMAP4Exception): pass