Recently I am not getting any email notification in nagios. I have tested it by sending emails manually from root user and nagios user and I have got the email successfully. But I am not any email alerts in case any issue so that I tested it by sending custom host notification from WEBUI, something seems to be wrong in the log. I hope someone can help me. Please find the logs below:

From Nagios Frontend Webui: (Tested it by sending custom host notification)

Sep 24 20:43:00 ubuntubackup-chennai sendmail[5923]: q8OFD0bP005923: Authentication-Warning: localhost.localdomain: nagios set sender to nagiosub@****.com using -r

Sep 24 20:43:00 ubuntubackup-chennai sendmail[5923]: q8OFD0bP005923: from=nagiosub@****.com, size=436, class=0, nrcpts=1, msgid=<5060787c.cbQWUMyq0G8H5/8r%nagiosub@****.com>, relay=nagios@localhost                   

Sep 24 20:43:00 ubuntubackup-chennai sendmail[5924]: q8OFD0JV005924: <[email protected]>... User unknown

Sep 24 20:43:00 ubuntubackup-chennai sendmail[5923]: q8OFD0bP005923: to=$, ctladdr=nagiosub@****.com (496/492), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30436, relay=[127.0.0.1] [127.0.0.1], dsn=5.1.1, stat=User unknown

Sep 24 20:43:00 ubuntubackup-chennai sendmail[5924]: q8OFD0JV005924: from=<nagiosub@****.com>, size=436, class=0, nrcpts=0, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]

Sep 24 20:43:00 ubuntubackup-chennai sendmail[5923]: q8OFD0bP005923: q8OFD0bQ005923: DSN: User unknown

Sep 24 20:43:01 ubuntubackup-chennai sendmail[5924]: q8OFD0JX005924: from=<>, size=2374, class=0, nrcpts=1, msgid=<[email protected]>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]

Sep 24 20:43:01 ubuntubackup-chennai sendmail[5923]: q8OFD0bQ005923: to=nagiosub@****.com, delay=00:00:01, xdelay=00:00:01, mailer=relay, pri=31460, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (q8OFD0JX005924 Message accepted for delivery)

Sep 24 20:43:02 ubuntubackup-chennai sendmail[5926]: q8OFD0JX005924: to=<nagiosub@****>, delay=00:00:02, xdelay=00:00:01, mailer=relay, pri=122374, relay=smtp10.netcore.co.in. [202.162.229.32], dsn=2.0.0, stat=Sent (_SMR_smtp12.netcore.co.in Ok: queued as 0797E19957)

As Nagios User From Terminal:

Sep 24 20:44:04 ubuntubackup-chennai sendmail[6067]: q8OFE4Th006067: Authentication-Warning: localhost.localdomain: nagios set sender to nagiosub@****.com using -r

Sep 24 20:44:04 ubuntubackup-chennai sendmail[6067]: q8OFE4Th006067: from=nagiosub@****.com, size=341, class=0, nrcpts=1, msgid=<506078bc.5x+q5X78H8WjVw2J%nagiosub@****.com>, relay=nagios@localhost

Sep 24 20:44:04 ubuntubackup-chennai sendmail[6068]: q8OFE4WN006068: from=<nagiosub@****.com>, size=614, class=0, nrcpts=1, msgid=<506078bc.5x+q5X78H8WjVw2J%nagiosub@****>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]

Sep 24 20:44:05 ubuntubackup-chennai sendmail[6067]: q8OFE4Th006067: to=karthick@****.com, ctladdr=nagiosub@**** (496/492), delay=00:00:01, xdelay=00:00:01, mailer=relay, pri=30341, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (q8OFE4WN006068 Message accepted for delivery)

Sep 24 20:44:05 ubuntubackup-chennai sendmail[6070]: q8OFE4WN006068: to=<karthick@****.com>, delay=00:00:01, xdelay=00:00:00, mailer=relay, pri=120614, relay=smtp10.netcore.co.in. [202.162.229.32], dsn=2.0.0, stat=Sent (_SMR_smtp9.netcore.co.in Ok: queued as 517CEF7E69)

As Root user from Terminal:

Sep 24 20:44:56 ubuntubackup-chennai sendmail[6167]: q8OFEtSo006167: from=root, size=281, class=0, nrcpts=1, msgid=<[email protected]>, relay=root@localhost

Sep 24 20:44:56 ubuntubackup-chennai sendmail[6168]: q8OFEuBX006168: from=<[email protected]>, size=555, class=0, nrcpts=1, msgid=<[email protected]>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]

Sep 24 20:44:56 ubuntubackup-chennai sendmail[6167]: q8OFEtSo006167: to=karthick@****, ctladdr=root (0/0), delay=00:00:01, xdelay=00:00:00, mailer=relay, pri=30281, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (q8OFEuBX006168 Message accepted for delivery)

Sep 24 20:44:56 ubuntubackup-chennai sendmail[6170]: q8OFEuBX006168: to=<karthick@****.com>, ctladdr=<[email protected]> (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=120555, relay=smtp10.netcore.co.in. [202.162.229.32], dsn=2.0.0, stat=Sent (_SMR_smtp12.netcore.co.in Ok: queued as 727A519942)

Note:

• Mail received from root user & nagios user but not from Nagios WEBUI.

Entry in hosts file: /etc/hosts

127.0.0.1               localhost.localdomain localhost ubuntubackup

::1             localhost6.localdomain6 localhost6