Blank originator

Hi…. i was new in Exchange server, so please give me a clue….

Ihave a mail server Ms Exchange 5.5, and have problem about exchange. The server is already have a Anti Virus Mcafee and always update new anti virus.

Sometimes Mcafee detect virus, in Internet Mail Service, Queues outbound messages a waiting delivery blank originator (not from our user). After that, the blank originator will coming more and more in Queues outbound messages. And make our user became the second priority…
User can’t send a message, only receive…..
I deleted a blank originator and our user came normally.

Please help me…..