diff -urN ../roundcubemail-1.5.2.orig/program/lib/Roundcube/rcube_imap.php ./program/lib/Roundcube/rcube_imap.php
--- ../roundcubemail-1.5.2.orig/program/lib/Roundcube/rcube_imap.php	2021-12-30 00:29:24.000000000 +0200
+++ ./program/lib/Roundcube/rcube_imap.php	2022-02-17 00:19:25.011073000 +0200
@@ -2306,6 +2306,12 @@
         else if (!empty($part->d_parameters['filename'])) {
             $filename_mime = $part->d_parameters['filename'];
         }
+        else if ((!empty($part->d_parameters['filename*'])) and (preg_match('/^([a-zA-Z\d\-]+)\'\'(.+)$/', $part->d_parameters['filename*'], $matches))) {
+            $filename_mime = sprintf("=?%s?Q?%s?=", $matches[1], preg_replace('/%([\da-fA-F]{2})/', '=$1', $matches[2]));
+            if (empty($part->charset)) {
+                $part->charset = $matches[1];
+            }
+        }
         // read 'name' after rfc2231 parameters as it may contain truncated filename (from Thunderbird)
         else if (!empty($part->ctype_parameters['name'])) {
             $filename_mime = $part->ctype_parameters['name'];
diff -urN ../roundcubemail-1.5.2.orig/program/lib/Roundcube/rcube_mime_decode.php ./program/lib/Roundcube/rcube_mime_decode.php
--- ../roundcubemail-1.5.2.orig/program/lib/Roundcube/rcube_mime_decode.php	2021-12-30 00:29:24.000000000 +0200
+++ ./program/lib/Roundcube/rcube_mime_decode.php	2022-02-17 00:25:35.075603000 +0200
@@ -402,6 +402,9 @@
         else if (!empty($part->ctype_parameters['name'])) {
             $filename = $part->ctype_parameters['name'];
         }
+        else if ((!empty($part->d_parameters['filename*'])) and (preg_match('/^([a-zA-Z\d\-]+)\'\'(.+)$/', $part->d_parameters['filename*'], $matches))) {
+            $filename = sprintf("=?%s?Q?%s?=", $matches[1], preg_replace('/%([\da-fA-F]{2})/', '=$1', $matches[2]));
+        }
 
         if (!empty($filename)) {
             if (empty($this->params['decode_headers'])) {