diff --git a/admin/tool/messageinbound/classes/manager.php b/admin/tool/messageinbound/classes/manager.php
index 46ae5d97c4a..e46a46b8cdd 100644
--- a/admin/tool/messageinbound/classes/manager.php
+++ b/admin/tool/messageinbound/classes/manager.php
@@ -95,6 +95,7 @@ class manager {
             'password' => $CFG->messageinbound_hostpass,
             'hostspec' => $CFG->messageinbound_host,
             'secure'   => $CFG->messageinbound_hostssl,
+            'debug'    => empty($CFG->debugimap) ? null : fopen('php://stderr', 'w'),
         );
 
         $this->client = new \Horde_Imap_Client_Socket($configuration);
diff --git a/config-dist.php b/config-dist.php
index 469884d211f..ea84afeec62 100644
--- a/config-dist.php
+++ b/config-dist.php
@@ -563,6 +563,9 @@ $CFG->admin = 'admin';
 // Prevent theme caching
 // $CFG->themedesignermode = true; // NOT FOR PRODUCTION SERVERS!
 //
+// Enable verbose debug information during fetching of email messages from IMAP server.
+// $CFG->debugimap = true;
+//
 // Prevent JS caching
 // $CFG->cachejs = false; // NOT FOR PRODUCTION SERVERS!
 //