To trigger reverse DNS (rDNS) queries with the opensource-socialnetwork (OSSN) platform, you can follow a few steps. Firstly, ensure that you have the necessary permissions and access to the server hosting the OSSN platform. Next, locate the specific function or module within the OSSN source code responsible for handling user profile information or registration. Look for the section where user IP addresses are recorded or stored. Within that section, incorporate the rDNS query functionality using appropriate programming techniques or by leveraging existing libraries. This will allow you to retrieve the reverse DNS information corresponding to the user's IP address. Finally, implement the necessary display or logging mechanism to showcase or store the rDNS results as desired within the OSSN platform. By following these steps, you can integrate rDNS queries seamlessly into the OSSN platform, enriching user profiles with valuable reverse DNS information.
The Web developer working on implementing the functionality to trigger rDNS queries with opensource-socialnetwork should have expertise in web development, programming languages, and server-side scripting.

https://www.php.net/manual/en/function.gethostbyname.php

I was wondering if there are function calls to get host's IP address, e.g. rDNS?

I am not sure what does this mean? what has it do with smtpConnect() what exactly you wanted to do?