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I have CentOS 6.7 with Apache, PHP and CakePHP 3.0 installed. I just checked up on my /var/log/maillog. I have this logged every 5min without fail. Does anyone know who's doing this and why? Or how I can identity who is doing this and why?

Apr 24 10:35:01 ip-1xx-xx-xx-1xx sendmail[30895]: u3OHZ16M030895: from=root, size=347, class=0, nrcpts=1, msgid=<201604241735.u3OHZ16M030895@ip-1xx-xx-xx-1xx.secureserver.net>, relay=root@localhost
Apr 24 10:35:01 ip-1xx-xx-xx-1xx sendmail[30896]: u3OHZ1UJ030896: from=<root@ip-1xx-xx-xx-1xx.secureserver.net>, size=674, class=0, nrcpts=1, msgid=<201604241735.u3OHZ16M030895@ip-1xx-xx-xx-1xx.secureserver.net>, proto=ESMTP, daemon=MTA, relay=localhost [127.0.0.1]
Apr 24 10:35:01 ip-1xx-xx-xx-1xx sendmail[30895]: u3OHZ16M030895: to=root, ctladdr=root (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30347, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (u3OHZ1UJ030896 Message accepted for delivery)
Apr 24 10:35:01 ip-1xx-xx-xx-1xx sendmail[30897]: u3OHZ1UJ030896: to=<root@ip-1xx-xx-xx-1xx.secureserver.net>, ctladdr=<root@ip-1xx-xx-xx-1xx.secureserver.net> (0/0), delay=00:00:00, xdelay=00:00:00, mailer=local, pri=30927, dsn=2.0.0, stat=Sent
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As you can see, once you group those log entries by internal message ID, those are email messages that stay within your server:

u3OHZ16M030895: from=root ...
u3OHZ16M030895: to=root ... (u3OHZ1UJ030896 Message accepted for delivery)

and

u3OHZ1UJ030896: from=<root@ip-1xx-xx-xx-1xx.secureserver.net> ...
u3OHZ1UJ030896: to=<root@ip-1xx-xx-xx-1xx.secureserver.net> ... mailer=local ... 

which mainly looks look sendmail rewriting the address from plain root to root@fully-qualified-hostname hence the two message ID's for a single message.

You would start by actually reading the mailbox for the root user ... An educated random guess would be a scheduled job (cron) that generates standard output.

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  • Well I have a cron job running every 5min, but it definitely does not explicitly send an e-mail. Maurizio seems to be addressing why a cron job would somehow generate an auto-email in his answer.
    – Joe C
    Apr 25 '16 at 16:29
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Hbruijn response seems to be correct, bsically, whenever any user in the machine (root or other) has a cript running in brtch mode without a window where toi address standard output messages, such a messages are addressed to @ address and, even, addressed to root, meanng "Warning: you have some process writing message you cannot red, so take care of email".

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  • Coincidentally I have my only cron job that I added running exactly every 5min. However that cron job is an extremely brief bash script that does NOT send any e-mails. Are you saying that even though its bash script does not explicitly send an e-mail it somehow causes an e-mail to be sent? If so then why? And what's the way to run a bash script in a cron without it generating an e-mail?
    – Joe C
    Apr 25 '16 at 16:26
  • @JoeC generally speaking, you'll need to append something to send the output to a bit bucket. For example: 0 1 5 10 * /path/to/script.sh >/dev/null 2>&1 For further details, see: cyberciti.biz/faq/disable-the-mail-alert-by-crontab-command
    – Mike B
    Apr 25 '16 at 17:26

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