diff --git a/bootstrap.php b/bootstrap.php
index 565b797..7e593e6 100644
--- a/bootstrap.php
+++ b/bootstrap.php
@@ -1613,3 +1613,14 @@ function imap2_utf8(string $string)
         return imap_utf8($string);
     }
 }
+
+/* For testing
+// A side-effectless version (functions only) of Roundcube's bootstrap.php
+require __DIR__ . '/rcube_bootstrap.php';
+require __DIR__ . '/roundcubemail/program/lib/Roundcube/rcube.php';
+require __DIR__ . '/roundcubemail/program/lib/Roundcube/rcube_mime_decode.php';
+require __DIR__ . '/roundcubemail/program/lib/Roundcube/rcube_charset.php';
+require __DIR__ . '/roundcubemail/program/lib/Roundcube/rcube_string_replacer.php';
+require __DIR__ . '/roundcubemail/program/lib/Roundcube/rcube_imap_generic.php';
+require __DIR__ . '/roundcubemail/program/lib/Roundcube/rcube_result_index.php';
+*/
diff --git a/composer.json b/composer.json
index b7f9a58..ecb86e7 100755
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,9 @@
     "zbateson/mail-mime-parser": "^2.2"
   },
   "require-dev": {
-    "phpunit/phpunit": "^6.5"
+    "phpunit/phpunit": "^6.5",
+    "phpstan/phpstan": "^1.10",
+    "pear/auth_sasl": "^1.1"
   },
   "suggest": {
     "ext-mbstring": "For best support/performance",
diff --git a/src/Mailbox.php b/src/Mailbox.php
index c72f110..b17b5b5 100644
--- a/src/Mailbox.php
+++ b/src/Mailbox.php
@@ -35,7 +35,7 @@ public static function check($imap)
             return imap_check($imap);
         }
 
-        trigger_error(Errors::invalidImapConnection(debug_backtrace(), 1), E_USER_WARNING);
+        trigger_error(Errors::invalidImapConnection(debug_backtrace(), 1, false), E_USER_WARNING);
 
         return false;
     }
@@ -245,13 +245,13 @@ public static function createMailbox($imap, $mailbox)
 
     public static function renameMailbox($imap, $from, $to)
     {
-        if (is_a($imap, Connection::class)) {
-            $client = $imap->getClient();
-
-            return $client->createFolder($mailbox);
+        if (!is_a($imap, Connection::class)) {
+            return Errors::invalidImapConnection(debug_backtrace(), 1, false);
         }
 
-        return imap_createmailbox($imap, $mailbox);
+        $client = $imap->getClient();
+
+        return $client->renameFolder($from, $to);
     }
 
     public static function deleteMailbox($imap, $mailbox)
diff --git a/src/Polyfill.php b/src/Polyfill.php
index 949e279..9ce0174 100644
--- a/src/Polyfill.php
+++ b/src/Polyfill.php
@@ -87,7 +87,7 @@ public static function rfc822WriteHeaders($string)
 
     public static function utf7Decode($string)
     {
-        return mb_convert_decoding($string, "UTF7-IMAP", "UTF-8");
+        return mb_convert_encoding($string, "UTF7-IMAP", "UTF-8");
     }
 
     public static function utf7Encode($string)
diff --git a/src/Roundcube/Charset.php b/src/Roundcube/Charset.php
index 99222a8..b776525 100644
--- a/src/Roundcube/Charset.php
+++ b/src/Roundcube/Charset.php
@@ -23,8 +23,8 @@
 
 namespace Javanile\Imap2\Roundcube;
 
-use Javanile\Imap2\ErrorException;
-use Javanile\Imap2\rcube;
+use ErrorException;
+use rcube;
 
 /**
  * Character sets conversion functionality
diff --git a/src/Roundcube/ImapClient.php b/src/Roundcube/ImapClient.php
index 6d61885..03e32ff 100644
--- a/src/Roundcube/ImapClient.php
+++ b/src/Roundcube/ImapClient.php
@@ -26,10 +26,10 @@
 
 namespace Javanile\Imap2\Roundcube;
 
-use Javanile\Imap2\Auth_SASL;
-use Javanile\Imap2\Exception;
-use Javanile\Imap2\GSSAPIContext;
-use Javanile\Imap2\KRB5CCache;
+use Auth_SASL;
+use Exception;
+use GSSAPIContext;
+use KRB5CCache;
 use Javanile\Imap2\rcube_message_header;
 use Javanile\Imap2\rcube_result_index;
 use Javanile\Imap2\rcube_result_thread;
diff --git a/src/Roundcube/Mime.php b/src/Roundcube/Mime.php
index f082ed4..17a7f64 100644
--- a/src/Roundcube/Mime.php
+++ b/src/Roundcube/Mime.php
@@ -21,8 +21,8 @@
 
 namespace Javanile\Imap2\Roundcube;
 
-use Javanile\Imap2\rcube;
-use Javanile\Imap2\rcube_mime_decode;
+use rcube;
+use rcube_mime_decode;
 
 /**
  * Class for parsing MIME messages
diff --git a/src/Roundcube/ResultIndex.php b/src/Roundcube/ResultIndex.php
index ce0a371..8c607d4 100644
--- a/src/Roundcube/ResultIndex.php
+++ b/src/Roundcube/ResultIndex.php
@@ -22,7 +22,7 @@
 namespace Javanile\Imap2\Roundcube;
 
 use Javanile\Imap2\Offset;
-use Javanile\Imap2\rcube_imap_generic;
+use rcube_imap_generic;
 
 /**
  * Class for accessing IMAP's SORT/SEARCH/ESEARCH result
diff --git a/src/Roundcube/ResultThread.php b/src/Roundcube/ResultThread.php
index e8a16f6..54b7a08 100644
--- a/src/Roundcube/ResultThread.php
+++ b/src/Roundcube/ResultThread.php
@@ -22,8 +22,8 @@
 namespace Javanile\Imap2\Roundcube;
 
 use Javanile\Imap2\Offset;
-use Javanile\Imap2\rcube_imap_generic;
-use Javanile\Imap2\rcube_result_index;
+use rcube_imap_generic;
+use rcube_result_index;
 
 /**
  * Class for accessing IMAP's THREAD result
@@ -427,7 +427,7 @@ public function get_parameters($param=null)
      */
     public function sort($index)
     {
-        $this->sort_order = $index->get_parameters('ORDER');
+        $this->order = $index->get_parameters('ORDER');
 
         if (empty($this->raw_data)) {
             return;
diff --git a/src/Roundcube/Utils.php b/src/Roundcube/Utils.php
index b5a83cc..7b5e779 100644
--- a/src/Roundcube/Utils.php
+++ b/src/Roundcube/Utils.php
@@ -21,12 +21,12 @@
 
 namespace Javanile\Imap2\Roundcube;
 
-use Javanile\Imap2\DateTime;
-use Javanile\Imap2\DateTimeZone;
-use Javanile\Imap2\Exception;
-use Javanile\Imap2\rcube;
-use Javanile\Imap2\rcube_charset;
-use Javanile\Imap2\rcube_string_replacer;
+use DateTime;
+use DateTimeZone;
+use Exception;
+use rcube;
+use rcube_charset;
+use rcube_string_replacer;
 
 /**
  * Utility class providing common functions