Custom header integration with DKIM

Hi,
I used https://github.com/langpavel/PhpSkelet/tree/master/Email/dkim before this plugin for sending mails with DKIM headers. Worked perfectly fine. While using postman plugin, need to send all wp mails with DKIM headers. Do u guys have any idea how to use the Additional Header to include DKIM headers. Added public key in my DNS.