diff --git a/sources/backend/caldav/caldav.php b/sources/backend/caldav/caldav.php
index a937381..9a3c19c 100644
--- a/sources/backend/caldav/caldav.php
+++ b/sources/backend/caldav/caldav.php
@@ -394,6 +394,19 @@ class BackendCalDAV extends BackendDiff {
         return $events;
     }
 
+    /**
+     * Resolves recipients
+     *
+     * @param SyncObject        $resolveRecipients
+     *
+     * @access public
+     * @return SyncObject       $resolveRecipients
+     */
+    public function ResolveRecipients($resolveRecipients) {
+        // TODO:
+        return false;
+    }
+
     /**
      * Indicates which AS version is supported by the backend.
      *
diff --git a/sources/backend/carddav/carddav.php b/sources/backend/carddav/carddav.php
index 653502d..53144e7 100644
--- a/sources/backend/carddav/carddav.php
+++ b/sources/backend/carddav/carddav.php
@@ -702,6 +702,20 @@ class BackendCardDAV extends BackendDiff implements ISearchProvider {
     }
 
 
+    /**
+     * Resolves recipients
+     *
+     * @param SyncObject        $resolveRecipients
+     *
+     * @access public
+     * @return SyncObject       $resolveRecipients
+     */
+    public function ResolveRecipients($resolveRecipients) {
+        // TODO:
+        return false;
+    }
+
+
     /**
      * Indicates which AS version is supported by the backend.
      *
diff --git a/sources/backend/combined/combined.php b/sources/backend/combined/combined.php
index c88e915..28d110e 100644
--- a/sources/backend/combined/combined.php
+++ b/sources/backend/combined/combined.php
@@ -393,6 +393,19 @@ class BackendCombined extends Backend implements ISearchProvider {
         return $backend->MeetingResponse($requestid, $this->GetBackendFolder($folderid), $response);
     }
 
+    /**
+     * Resolves recipients
+     *
+     * @param SyncObject        $resolveRecipients
+     *
+     * @access public
+     * @return SyncObject       $resolveRecipients
+     */
+    public function ResolveRecipients($resolveRecipients) {
+        // TODO:
+        return false;
+    }
+
 
     /**
      * Deletes all contents of the specified folder.
diff --git a/sources/backend/imap/imap.php b/sources/backend/imap/imap.php
index 5f2a08e..42e04f0 100644
--- a/sources/backend/imap/imap.php
+++ b/sources/backend/imap/imap.php
@@ -1730,6 +1730,20 @@ class BackendIMAP extends BackendDiff implements ISearchProvider {
     }
 
 
+    /**
+     * Resolves recipients
+     *
+     * @param SyncObject        $resolveRecipients
+     *
+     * @access public
+     * @return SyncObject       $resolveRecipients
+     */
+    public function ResolveRecipients($resolveRecipients) {
+        // TODO:
+        return false;
+    }
+
+
     /**
      * Returns the email address and the display name of the user. Used by autodiscover.
      *
@@ -1841,7 +1855,7 @@ class BackendIMAP extends BackendDiff implements ISearchProvider {
         $search = true;
 
         if (empty($searchFolderId)) {
-            $searchFolderId = $this->getFolderIdFromImapId('INBOX');
+            $searchFolderId = $this->getFolderIdFromImapId($this->create_name_folder(IMAP_FOLDER_INBOX), false);
         }
 
         // Convert searchFolderId to IMAP id
@@ -2049,20 +2063,36 @@ class BackendIMAP extends BackendDiff implements ISearchProvider {
      * @access protected
      * @return string       hex folder id
      */
-    protected function getFolderIdFromImapId($imapid) {
+    protected function getFolderIdFromImapId($imapid, $case_sensitive = true) {
         $this->InitializePermanentStorage();
 
-        if (isset($this->permanentStorage->fmFimapFid)) {
-            if (isset($this->permanentStorage->fmFimapFid[$imapid])) {
-                $folderid = $this->permanentStorage->fmFimapFid[$imapid];
-                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFolderIdFromImapId('%s') = %s", $imapid, $folderid));
-                return $folderid;
-            }
-            else {
-                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFolderIdFromImapId('%s') = %s", $imapid, 'not found'));
-                return false;
+        if ($case_sensitive) {
+            if (isset($this->permanentStorage->fmFimapFid)) {
+                if (isset($this->permanentStorage->fmFimapFid[$imapid])) {
+                    $folderid = $this->permanentStorage->fmFimapFid[$imapid];
+                    ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFolderIdFromImapId('%s') = %s", $imapid, $folderid));
+                    return $folderid;
+                }
+                else {
+                    ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFolderIdFromImapId('%s') = %s", $imapid, 'not found'));
+                    return false;
+                }
             }
         }
+        else {
+            if (isset($this->permanentStorage->fmFimapFidLowercase)) {
+                if (isset($this->permanentStorage->fmFimapFidLowercase[strtolower($imapid)])) {
+                    $folderid = $this->permanentStorage->fmFimapFidLowercase[strtolower($imapid)];
+                    ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFolderIdFromImapId('%s', false) = %s", $imapid, $folderid));
+                    return $folderid;
+                }
+                else {
+                    ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFolderIdFromImapId('%s', false) = %s", $imapid, 'not found'));
+                    return false;
+                }
+            }
+        }
+
         ZLog::Write(LOGLEVEL_WARN, sprintf("BackendIMAP->getFolderIdFromImapId('%s') = %s", $imapid, 'not initialized!'));
         return false;
     }
@@ -2103,6 +2133,13 @@ class BackendIMAP extends BackendDiff implements ISearchProvider {
             $b = $this->permanentStorage->fmFimapFid;
             $b[$imapid] = $folderid;
             $this->permanentStorage->fmFimapFid = $b;
+
+            if (!isset($this->permanentStorage->fmFimapFidLowercase))
+                $this->permanentStorage->fmFimapFidLowercase = array();
+
+            $c = $this->permanentStorage->fmFimapFidLowercase;
+            $c[strtolower($imapid)] = $folderid;
+            $this->permanentStorage->fmFimapFidLowercase = $c;
         }
 
         ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->convertImapId('%s') = %s", $imapid, $folderid));
@@ -2328,7 +2365,7 @@ class BackendIMAP extends BackendDiff implements ISearchProvider {
      */
     protected function checkIfIMAPFolder($folderName) {
         $folder_name = $folderName;
-        if (defined(IMAP_FOLDER_PREFIX) && strlen(IMAP_FOLDER_PREFIX) > 0) {
+        if (defined('IMAP_FOLDER_PREFIX') && strlen(IMAP_FOLDER_PREFIX) > 0) {
             // TODO: We don't care about the inbox exception with the prefix, because we won't check inbox
             $folder_name = IMAP_FOLDER_PREFIX . $this->getServerDelimiter() . $folder_name;
         }
@@ -2470,7 +2507,7 @@ class BackendIMAP extends BackendDiff implements ISearchProvider {
         }
 
         if ($this->sentID === false) {
-            $this->sentID = $this->getFolderIdFromImapId($this->create_name_folder(IMAP_FOLDER_SENT));
+            $this->sentID = $this->getFolderIdFromImapId($this->create_name_folder(IMAP_FOLDER_SENT), false);
         }
 
         $saved = false;
diff --git a/sources/backend/ldap/ldap.php b/sources/backend/ldap/ldap.php
index 2ad52c2..af1584b 100644
--- a/sources/backend/ldap/ldap.php
+++ b/sources/backend/ldap/ldap.php
@@ -9,8 +9,8 @@
 * Created   :   07.04.2012
 *
 * Copyright 2012 - 2014 Jean-Louis Dupond
-*
 * Jean-Louis Dupond released this code as AGPLv3 here: https://github.com/dupondje/PHP-Push-2/issues/93
+* Copyright 2015 - Francisco Miguel Biete
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License, version 3,
@@ -565,6 +565,19 @@ class BackendLDAP extends BackendDiff {
         return false;
     }
 
+    /**
+     * Resolves recipients
+     *
+     * @param SyncObject        $resolveRecipients
+     *
+     * @access public
+     * @return SyncObject       $resolveRecipients
+     */
+    public function ResolveRecipients($resolveRecipients) {
+        // TODO:
+        return false;
+    }
+
     /**
      * Indicates which AS version is supported by the backend.
      *
diff --git a/sources/index.php b/sources/index.php
index 0df69eb..1568a87 100644
--- a/sources/index.php
+++ b/sources/index.php
@@ -89,7 +89,7 @@ if (defined('LOG_MEMORY_PROFILER') && LOG_MEMORY_PROFILER) {
         // Stop here if this is an OPTIONS request
         if (Request::IsMethodOPTIONS()) {
             if (!$autenticationInfo || !$GETUser) {
-                throw new AuthenticationRequiredException("Access denied. Please send authorisation information");
+                throw new AuthenticationRequiredException("Access denied. Please send authentication information");
             }
             else {
                 throw new NoPostRequestException("Options request", NoPostRequestException::OPTIONS_REQUEST);