BIG-IP sending cron related mail to SMTP server every 5 minutes

BIG-IP ltm (Ver. 12.1.0) I configured ssmtp to send locally generated emails to SMTP server. The purpose is to test SNMP trap alerts to send email notifications. After the above configuration, I noticed that my BIG-IP is sending cron related mail ↓ to SMTP server that I had configured earlier.

I tried some of the fixes/solutions in the AskF5 knowledge center/resources, but to no avail. Some of the things I tried:

1. Changed the permission of /var/log/sa6/sa
2. Modified MAILTO=root to MAILTO="" in every possible cron jobs.

3. https://devcentral.f5.com/questions/err-ssmtp-48399

   https://devcentral.f5.com/questions/just-upgraded-to-121-and-getting-many-cron-emails-47141

Has anyone come accross something like this? I want to get rid of this. Seeking your help. Thank you!

From root@BIG-IP-01.localdomain  Wed Dec 13 15:30:02 2017
Return-Path: [root@BIG-IP-01.localdomain](/mailto:root@BIG-IP-01.localdomain)
X-Original-To: postmaster@BIG-IP-01.localdomain
Delivered-To: postmaster@BIG-IP-01.localdomain
Received: from BIG-IP-01.localdomain (unknown [10.35.143.14])
        by mail0.example.jp (Postfix) with SMTP id 76AD0400D6DA
        for [postmaster@BIG-IP-01.localdomain](/mailto:postmaster@BIG-IP-01.localdomain); Wed, 13 Dec 2017 15:30:01 +0900 (JST)
Received: by BIG-IP-01.localdomain (sSMTP sendmail emulation); Wed, 13 Dec 2017 15:30:01 +0900
From: "root" [root@BIG-IP-01.localdomain](/mailto:root@BIG-IP-01.localdomain)
Date: Wed, 13 Dec 2017 15:30:01 +0900
To: root
Subject: Cron  /usr/lib/sa/sa1 1 1
Content-Type: text/plain; charset=UTF-8
Auto-Submitted: auto-generated
X-Cron-Env: 
X-Cron-Env: 
X-Cron-Env: 
X-Cron-Env: 
X-Cron-Env: 
X-Cron-Env: 

Cannot open /var/log/sa6/sa: Permission denied