backslash in username does not work for IMAP login
I need to access an exchange server via IMAP. My username has the form username@domain\\special_mailbox .
Authentication with just username for the personal mailbox works fine but not for the special mailbox with the backslash syntax above.
I tried two backslashes since I suspected some java string escaping problem, but that did not work either.

diff --git a/k9mail-library/src/main/java/com/fsck/k9/mail/store/imap/ImapConnection.java b/k9mail-library/src/main/java/com/fsck/k9/mail/store/imap/ImapConnection.java
index a81408755..ada1a1f53 100644
--- a/k9mail-library/src/main/java/com/fsck/k9/mail/store/imap/ImapConnection.java
+++ b/k9mail-library/src/main/java/com/fsck/k9/mail/store/imap/ImapConnection.java
@@ -364,6 +364,14 @@ class ImapConnection {
         }
     }
 
+    protected void saslAuthPlainWithLoginFallback() throws IOException, MessagingException {
+        try {
+            saslAuthPlain();
+        } catch (AuthenticationFailedException e) {
+            login();
+        }
+    }
+
     protected ImapResponse readContinuationResponse(String tag)
             throws IOException, MessagingException {
         ImapResponse response;
@@ -510,7 +518,7 @@ class ImapConnection {
 
             case PLAIN:
                 if (hasCapability(CAPABILITY_AUTH_PLAIN)) {
-                    saslAuthPlain();
+                    saslAuthPlainWithLoginFallback();
                 } else if (!hasCapability(CAPABILITY_LOGINDISABLED)) {
                     login();
                 } else {
['k9mail-library/src/main/java/com/fsck/k9/mail/store/imap/ImapConnection.java']