From b1bd138c3dba30458c59599533b5b71a41b9e297 Mon Sep 17 00:00:00 2001
From: Steven Ngesera <muhngesteven@gmail.com>
Date: Fri, 9 Aug 2024 03:20:49 +0300
Subject: [PATCH] checking if the server supports custom headers

---
 modules/imap/hm-imap.php | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/modules/imap/hm-imap.php b/modules/imap/hm-imap.php
index 97261ddd7a..b8bbd4ece1 100644
--- a/modules/imap/hm-imap.php
+++ b/modules/imap/hm-imap.php
@@ -1099,7 +1099,7 @@ public function search($target='ALL', $uids=false, $terms=array(), $esearch=arra
             if ($only_auto_bcc) {
                $fld .= ' HEADER X-Auto-Bcc cypht';
             }
-            if (!mb_strstr($this->server, 'yahoo') && $exclude_auto_bcc) {
+            if ($this->server_supports_custom_headers() && !mb_strstr($this->server, 'yahoo') && $exclude_auto_bcc) {
                $fld .= ' NOT HEADER X-Auto-Bcc cypht';
             }
             $esearch_enabled = false;
@@ -2213,5 +2213,42 @@ public function get_folder_list_by_level($level='', $only_subscribed=false, $wit
             }
             return $result;
         }
+
+        /**
+         * test if the server supports searching by custom headers
+         * @return boolean true is the server supports searching by custom headers
+         */
+        protected function server_supports_custom_headers() {
+            $test_command = 'UID SEARCH HEADER "X-NonExistent-Header" "test"'."\r\n";
+            $this->send_command($test_command);
+            $response = $this->get_response(false, true);
+            $status = $this->check_response($response, true);
+
+            // Keywords that indicate the header search is not supported
+            $keywords = ['is', 'not', 'supported.'];
+
+            if (!$status) {
+                return false;
+            }
+
+            // Flatten the response array to a single array of strings
+            $flattened_response = array_reduce($response, 'array_merge', []);
+
+            // Check if all keywords are present in the flattened response
+            $sequence_match = true;
+            foreach ($keywords as $keyword) {
+                if (!in_array($keyword, $flattened_response)) {
+                    $sequence_match = false;
+                    break;
+                }
+            }
+
+            // If all keywords are found, the header search is not supported
+            if ($sequence_match) {
+                return false;
+            }
+
+            return true;
+        }
     }
 }