When you are unavailable and user sends a message, require them to enter a name!
I have customers that, if I'm offline, will send a message with NO CONTACT INFO, not even a name. If they haven't set up a name in the contact info, prompt for one before allowing them to send a message.
Otherwise, I can never get back to them and they think I'm not being responsive.

Thanks for reaching out. You currently have the “Ask Customer for Contact Info” setting set to “Never”.
You can change the contact info setting in the administrator control panel (http://admin.instanthousecall.com).
Scroll down to Manage Specialists, then move the green dot to either “Always” or “New Customers”.
Should do the trick. Anything else you need, just say the word.