phpList.org

Phplist + zimbra mail sending problem

I am getting the below error while sending mail through zimbra (version 8.7)

Feb 9 17:22:36 mail postfix/smtpd[8412]: lost connection after STARTTLS from mail.gipl.in[203.77.201.90]
Feb 9 17:22:36 mail postfix/smtpd[8412]: disconnect from mail.xxx.xx[xxx.xxx.xxx.xxx.] ehlo=1 starttls=0/1 commands=1/2
Feb 9 17:22:37 mail postfix/postscreen[7580]: CONNECT from [xxx.xxx.xxx.xxx]:38722 to [203.77.201.90]:25
Feb 9 17:22:37 mail postfix/postscreen[7580]: WHITELISTED [xxx.xxx.xxx.xxx]:38722
Feb 9 17:22:37 mail postfix/smtpd[8412]: connect from mail.xxx.xx[xxx.xxx.xxx.xxx]
Feb 9 17:22:37 mail postfix/smtpd[8412]: SSL_accept error from mail.xxx.xx[xxx.xxx.xxx.xxx]: 0
Feb 9 17:22:37 mail postfix/smtpd[8412]: warning: TLS library problem: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca:s3_pkt.c:1494:SSL alert number 48:

My PHP list conf setting

define(‘PHPMAILERHOST’, ‘mail.xxx.xx’);
define(‘PHPMAILER’,1);
define(“PHPMAILER_SECURE”,‘TLS’);
$phpmailer_smtpuser = ‘xxxx@xxx.xx’;
$phpmailer_smtppassword = ‘xxxxxxx’;
$phpmailer_smtpport = ‘587’;

@rohit googling for the warning message shows this explanation https://support.plesk.com/hc/en-us/articles/213387009-Unable-to-send-mail-via-SSL-warning-TLS-library-problem-31990