Hi,
Just mentioning this as a possible idea to be implemented with JReviews
https://www.jreviews.com ( I am the developer ). It integrates with EasySocial so activities appear in the ES stream and the listing (job opening) author can link back to the ES profile. You can use JReviews to let users with a specific user group in Joomla to post listings in a "job openings" category, and users could use the "send inquiry" (can be renamed to something else) feature to apply, and if you want them to upload their resume, they could do that via the "review" form where they could upload an attachment that can be set to be visible to Admins only.
If you want people to be able to message the job opening poster through ES messages, then that can also be achieved through a
developer filter.