You can open the record for that contact - employee - and click on his/her e-mail address:
This will start RC client with e-mail address already populated:
Besides - in RC just start typing the name of the person and it will search EPESI's CRM Contacts and will autocomplete the address:
Roundcube was modified in EPESI to use CRM contacts as addressbook.
But if you are using e-mail in EPESI to communicate with your employees than you are missing the entire idea:
e-mail in EPESI should be used ONLY to communicate with the "outside world" - people who don't have access to your CRM.
All communication with your employees = co-workers = EPESI users - should be happening without e-mail - you have tasks, calendar, notes, shoutbox, etc. Using e-mail internally makes no sense.