This indicates that you are using a server using PHP 5.6 or above and the local SMTP of your hosting account has issue with the domain certificate.
Changes to PHP 5.6 require a valid, correctly issued and set up SSL certificate.  This is outside of the control of arpReach


Generally a deeper check will show an error similar to the following:


Peer certificate CN=`*.server-host-name.com' did not match expected CN=`your-domain-name.com'


The solution is to either use the servers sendmail facility, but the best solution is to contact your hosting company and ask them to fix the certificate issue.


If your hosting company have a valid SSL certificate for the server root (the hostname of the server you are using) you may well be required to use a valid username and password along with the SMTP mailer something like:

mail.serverhostname.tld  where serverhostname.tld is the server hostname which the SSL certificate covers.  


Your hosting company will advise.


More  info:
https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting#php-56-certificate-verification-failure