Disadvantages to receive and send mails

Hello! 

I am having a problem with sending and receiving emails in my company, the exchange (2007) server apparently has no problems, and the Outlook client stations indicate that they are connected to it. If I try to send an email does not generate any error and also not in the outbox, appears as sent but is never received. We never had this happen and did not know what to do to determine what is happening. Please valuable assistance. 

Best Regards,