diff -r 8f85262fbe8a Lib/imaplib.py
--- a/Lib/imaplib.py	Sun Jul 06 02:24:24 2014 -0400
+++ b/Lib/imaplib.py	Wed Jul 16 17:19:49 2014 -0700
@@ -108,7 +108,13 @@
         br'"')
 Literal = re.compile(br'.*{(?P<size>\d+)}$', re.ASCII)
 MapCRLF = re.compile(br'\r\n|\r|\n')
-Response_code = re.compile(br'\[(?P<type>[A-Z-]+)( (?P<data>[^\]]*))?\]')
+
+"""
+We don't exclude the ']' character, even though it violates the RFC. This
+is because popular IMAP servers, such as Gmail, allow flags with ']'. Thus,
+we are purposefully violating the RFC for backward compatibility reasons.
+"""
+Response_code = re.compile(br'\[(?P<type>[A-Z-]+)( (?P<data>.*))?\]')
 Untagged_response = re.compile(br'\* (?P<type>[A-Z-]+)( (?P<data>.*))?')
 Untagged_status = re.compile(
     br'\* (?P<data>\d+) (?P<type>[A-Z-]+)( (?P<data2>.*))?', re.ASCII)