Does anyone know of plugins or other, a way of allowing my site authors to send and receive emails using the email set up @mysite.com instead of giving access to my hosting control panel? I'm looking for a secure way to allow authors to receive emails and be able to reply to them from within wordpress, it would need the option to be able to delete spam too.
What kind of control panel are you using. If its cpanel, you can give them access to check webmail for specific email accounts without giving them access to the entire control panel.
may be it's nice for you: http://www.thewindowsclub.com/how-to-create-a-custom-email-id-for-your-domain-with-hotmail
you can create the webmail accounts on your hosting account. This will create @domain.com email accounts that you can give to your authors. You can also manage these accounts with Google acounts if you want