SSL error in Exim log: "BIO routines:FILE_CTRL:system lib"

Symptoms

Email cannot be sent to your domain, and the Exim log shows an error similar to the following.

2024-03-18 21:02:57 TLS error on connection from host.domain.net (mail.domain.tld) [203.0.113.2]:61369 (SSL_accept): error:20074002:BIO routines:file_ctrl:system lib

Description

This error occurs when the certificate file has incorrect ownership.

Workaround

1. Access the server's command line as the 'root' user via SSH or "Terminal" in WHM.

2. Run the following command.

   find /var/cpanel/ssl/domain_tls -type f -exec chown root:mail {} \;