Group Mailbox Management

My company is a small organization with office strength of 15-20 people. We have a group email id. Around 10 people check the inbox daily through Outlook Express.
Now the problem we have is that we cannot keep track of all mails received in our inbox because when each individual is sending mail, those mails would get saved in their Outlook Express personal pc. Other people would not come to know unless its communicated verbally.
Can anyone suggest a solution where all of us can keep a track of any enquiry coming in and responses going out.