I agree with JDavis for moving to the Symantec Messaging Gateway(SMG) as the SMTP 5 is a very old product at this point in time. The SMG is a physical appliance or a virtual appliance. The SMG supports VMware ESX and ESXi but does not have support for MS hyper-v at this point in time.
For the SMTP 5 product, I would recommend that you make sure that sms mysql service is running. Also take a look at the following document.
http://www.symantec.com/business/support/index?page=content&id=TECH82759