Debian 8.7.1 - Postfix cerificate error

[garfield]

I've installed a Debian 8.7.1 and want to send mails using a relayhost and phpmailer. With Debian 6 it was no issue but now, with Debian 8 and PHP version 5.6.29 I get next error on the relayserver:

/var/log/maillog

2017 Apr 10 13:00:34 <relayserver> sendmail[4346]: STARTTLS=server, error: accept failed=0, SSL_error=1, errno=0, retry=-1
2017 Apr 10 13:00:34 <relayserver> sendmail[4346]: STARTTLS=server: 4346:error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca:s3_pkt.cSSL alert number 48
2017 Apr 10 13:00:34 <relayserver> sendmail[4346]: v3AB0Ylc004346: [<serverip>] did not issue MAIL/EXPN/VRFY/ETRN during connection to TLSMTA

PHPMailer on de Debian 8.7.1-server

[Mon Apr 10 13:00:34.537306 2017] [:error] [pid 862] [client <myip>:52187] PHP Fatal error: Uncaught exception 'phpmailerException' with message 'SMTP connect() failed.' in /var/www/html/test_mail/class.phpmailer.php:1465\nStack trace:\n#0 /var/www/html/test_mail/class.phpmailer.php(1301): PHPMailer->smtpSend('Date: Mon, 10 A...', 'Test\\n')\n#1 /var/www/html/test_mail/class.phpmailer.php(1181): PHPMailer->postSend()\n#2 /var/www/html/test_mail/mail.php(21): PHPMailer->send()\n#3 /var/www/html/test_mail/index.php(9): mail_test('<mydest>@...', '<myto>', '<myfrom>....', '<myname>', 'Test 2017-04-10', 'Test')\n#4 {main}\n thrown in /var/www/html/test_mail/class.phpmailer.php on line 1465

I tried making my own self-signed certificate but it does not work. I tried this tutorial:
https://www.linode.com/docs/security/ss ... and-ubuntu

What am I doing wrong and how can I fix it?

[bigrigdriver]

Try these instructions.
http://giantdorks.org/alain/fix-for-pos ... tls-error/