Email from fail2ban is deferred, but CMS email is delivered

July 30, 2015 623 views
Email Security Ubuntu

In the list of mail, there are now 66 messages like this. Fail2ban is working, and trying to send notification emails, but they are getting deferred. The CMS, however, is able to send emails with no problem (such as forgot password emails). (Email addresses and domains changed to protect the guilty.)

----- Transcript of session follows -----
<abc@xyz.com>... Deferred
Warning: message still undelivered after 4 hours
Will keep trying until message is 5 days old
550 5.1.1 <fail2ban@example.com>... User unknown

Part 2:
Content-Type: message/delivery-status

Part 3:
Content-Type: text/rfc822-headers

Return-Path: <fail2ban@example.com>
Received: from example.com (localhost [])
    by example.com (8.14.4/8.14.4/Debian-8) with ESMTP id t6L0f2g4017263
    for <abc@xyz.com>; Mon, 20 Jul 2015 20:41:02 -0400
Received: (from root@localhost)
    by example.com (8.14.4/8.14.4/Submit) id t6L0f1vR017257
    for abc@xyz.com; Mon, 20 Jul 2015 20:41:01 -0400
Message-Id: <201507210041.92d3d7cbb02@example.com>
Subject: [Fail2Ban] sshd: banned [IP ADDRESS] from example.com
Date: Tue, 21 Jul 2015 00:41:01 +0000
From: Fail2Ban <fail2ban@example.com>
To: abc@xyz.com
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