Our server does virus and spam filtering.  But there is a point where files are so large that for our servers to scan them it would put entirely too much of a load on the system.  To avoid that, any emails that are over 2 meg in size will not be scanned.  ***UNCHECKED*** is to tell you that the email has not gone through the filtering process.  In otherwords, it may contain a virus or it may be spam.  So practicing standard email precautions is in order.