Gerardo,
No disrespect meant here but if your staff is not checking messages in a timely manner, than that person needs to be talked to. Either that or this person is getting overwhelmed with the volume of messages? If it's the latter, have you considered using the option to change the color of your subject when it's sent? ie Red, green or blue? This way you could make important messages have the subject "re" in green?
In the new message screen, you can change the color of the message sent by choosing a color next to the "Pull Chart" button.
You can check to see if your messages have been acted on by checking your outbox. If the message you sent hasn't been opened, it will be there. That's the best solution I can come up with.
Hope this helps
