Hello, I am currently using the *Koha 21.05 version* with MariaDB. For the last two months, some (not all) of my users are not able to receive *only Item due reminder and Advance notice email*. I am using Postfix MTA. Users are getting other email notifications like checkout, checkin, membership notifications, etc. Please suggest to me the possible solutions, if any. *One of the failed issues is attached below for your reference.* As per the message below, it seems to be a firewall Issue. But my IT team told me it is not a firewall Issue. * Delivery Failure Notification Message:* From: <(unknown sender)> Date: Wed, 14 Dec, 2022, 7:45 am Subject: Delivery Failure Notification To: <infolibrary@xxx.xx.in> Sophos XG Firewall was unable to send the following mail: ---------------------- From: <infolibrary@xxx.xx.in> MessageID: <16709841111.BB6A.31044@koha.xxx.yy.in> Sent on: 2022-12-14 07:37:53 Mail delivery to following recipients failed: 00pp009@xxx.xx.in - Internal Server Error Received: from localhost.localdomain (localhost [IPv6:::1]) by koha.xxx.yy.in (Postfix) with ESMTP id 55ED91A40C45 for <00pp00@xxx.xx.in>; Wed, 14 Dec 2022 07:45:11 +0530 (IST) Date: Wed, 14 Dec 2022 07:45:11 +0530 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Advance Notice of Book(s) Due From: infolibrary@xxx.xx.in To: 00pp00@xxx.xx.in Reply-To: infolibrary@xxx.xx.in> X-Mailer: Koha Message-ID: <16709841111.BB6A.31044@ koha.xxx.yy.in> Dear Mr. Raj Kumar, The following book(s) will be due soon: Title: The=20 Author: Guillebeau, Chris=20 Accession No.: 71119 Due Date : 16/12/2022 23:59 --- Thank you **************************************************** Regards, Dr. Sambhunath Sahoo / डॉ सम्भुनाथ साहु Assistant Librarian / सहायक पुस्तकालयाध्यक्ष, Central Library / केन्द्रीय पुस्तकालय, 4th Floor, Administrative Building / चौथा मंजिल, प्रशासनिक भवन Indian Institute of Technology Bhubaneswar / भारतीय प्रौद्योगिकी संस्थान भुवनेश्वर Argul, Khurda, Odisha / आरगुल, खुर्दा, ओड़िशा, 752050 (India) *ORCID ID:* 0000-0001-9162-879X *Researcher ID:* K-4446-2018 *Scopus ID:* 57222542160 ****************************************************