Broken MTA

Dear Elgg Community Developers, and Helpers,

I am running elgg Elgg 2.3.14 LTS Release  (July 24, 2019). After installing and getting the site up and running for 2 months approx, I realized User on Registration were not being sent a validation email. I am running PHP 5.6.

On investigation, I found out that under basic settings  I had setup during site installation, but in HTML Email Handler Plugin I had -f setup.

So, I have corrected both the settings to and with -f in  HTML Email Handler Plugin.

Flushed the site and upgraded, but still the same issue. So, I set the "$CONFIG->broken_mta = false;" to true and same issue.

My Sendmail Path: is /usr/sbin/sendmail 

Did a MTA Test using elgg script. The url is

Get the following:

Attempting to email
ERROR! PHP could not deliver email to your MTA. Check that your PHP settings are correct for your MTA and your MTA will deliver email.

PHP 5.6 ini file shows

sendmail_from no value no value
sendmail_path /usr/sbin/sendmail -t -i  /usr/sbin/sendmail -t -i 

 So, experimented with values like -t -i -f in HTML Email Handler still the same issue.  

Then I tried disabling HTML Email Handler Plugin and same issue. Disabled all the plugins except Bundled, same issued.

Could it be that in database respective field / table / col where the email is set incorrect? or may be core elgg file is corrupt? Can someone please help?