Prevent role sending messages, but allow them to reply

This plugin was suggested to me in another topic as a possible part of a job board I'm trying to put together. I'm wondering if the following is possible with the plugin OOTB, or if some custom coding would be required.

I have 2 user roles, Employee and Employer.
Employers can: Start new conversations, Receive, Reply
Employees can: Reply, receive

The idea is that in my use case, employees might spam employers with "please give me a job" messages, but turning it off completely for them might mean they can't reply.