diff -urN ../automatic_addressbook-0.4.3.orig/automatic_addressbook.php ./automatic_addressbook.php
--- ../automatic_addressbook-0.4.3.orig/automatic_addressbook.php	2017-01-26 10:10:28.000000000 +0200
+++ ./automatic_addressbook.php	2023-03-16 14:57:47.440630000 +0200
@@ -123,15 +123,15 @@
         if (!class_exists('rcube_mime')) { // RC < 0.8 compatibility code
             $IMAP = new rcube_imap(null);
             $all_recipients = array_merge(
-                $IMAP->decode_address_list($headers['To'], null, true, $headers['charset']),
-                $IMAP->decode_address_list($headers['Cc'], null, true, $headers['charset']),
-                $IMAP->decode_address_list($headers['Bcc'], null, true, $headers['charset'])
+                (isset($headers['To'])) ? $IMAP->decode_address_list($headers['To'], null, true, (isset($headers['charset'])) ? $headers['charset'] : null) : [],
+                (isset($headers['Cc'])) ? $IMAP->decode_address_list($headers['Cc'], null, true, (isset($headers['charset'])) ? $headers['charset'] : null) : [],
+                (isset($headers['Bcc'])) ? $IMAP->decode_address_list($headers['Bcc'], null, true, (isset($headers['charset'])) ? $headers['charset'] : null) : []
             );
         } else {
             $all_recipients = array_merge(
-                rcube_mime::decode_address_list($headers['To'], null, true, $headers['charset']),
-                rcube_mime::decode_address_list($headers['Cc'], null, true, $headers['charset']),
-                rcube_mime::decode_address_list($headers['Bcc'], null, true, $headers['charset'])
+                (isset($headers['To'])) ? rcube_mime::decode_address_list($headers['To'], null, true, (isset($headers['charset'])) ? $headers['charset'] : null) : [],
+                (isset($headers['Cc'])) ? rcube_mime::decode_address_list($headers['Cc'], null, true, (isset($headers['charset'])) ? $headers['charset'] : null) : [],
+                (isset($headers['Bcc'])) ? rcube_mime::decode_address_list($headers['Bcc'], null, true, (isset($headers['charset'])) ? $headers['charset'] : null) : []
             );
         }
 
@@ -284,7 +284,7 @@
         if ($args['source'] !== $this->abook_id) {
             foreach (array('email:home', 'email:work', 'email:other') as $email_field) {
                 // Would trigger a warning with rc 0.5 without this if
-                if ($args['record'][$email_field]) {
+                if (!empty($args['record'][$email_field])) {
                     foreach ($args['record'][$email_field] as $email) {
                         $contact_emails[] = $email;
                     }