If PHP scripts running under an old version of the language fail to connect to SMTP server under Directadmin, and in logs can you see lines containing "TLS error on connection from hostname":
2020-02-20 00:30:02 TLS error on connection from localhost (www.poralix.com) [127.0.0.1] (SSL_accept): error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol 2020-02-20 00:33:01 TLS error on connection from localhost (www.poralix.com) [127.0.0.1] (SSL_accept): error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol 2020-02-20 00:50:53 TLS error on connection from localhost (www.poralix.com) [127.0.0.1] (SSL_accept): error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol 2020-02-20 00:55:09 TLS error on connection from localhost (www.poralix.com) [127.0.0.1] (SSL_accept): error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol 2020-02-20 02:22:12 TLS error on connection from localhost (www.poralix.com) [127.0.0.1] (SSL_accept): error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol 2020-02-20 03:24:59 TLS error on connection from localhost (www.poralix.com) [127.0.0.1] (SSL_accept): error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol
here is a possible fix.
For this run as root:
touch /etc/exim.variables.conf.custom echo 'openssl_options = +no_sslv2 +no_sslv3' >> /etc/exim.variables.conf.custom echo 'tls_require_ciphers=ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS' >> /etc/exim.variables.conf.custom
cd /usr/local/directadmin/custombuild/ ./build update ./build exim_conf
Please note TLSv1.0 and TLSv1.1 are considered to be deprecated and insecure. And if enabling them is the only possible solution for you, then you do it only on your own risk.
That's it.