Recieving external spam with external email not working

I have a interesting problem. I am recieving what seems to be external spam, but due to a dns issue we currently  cannot recieve external mail. What virus or spyware couold do this and how would I locate it.
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smnphoenixAsked:
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zerofieldConnect With a Mentor Commented:
if you arent receiving external email, or arent supposed to, sniff port 25 of your mailserver.  it's supposed to be very limited activity now anyway according to you.

if an upstream DNS server has cached your IP, and you're still online, it could just be "real" spam from the outside world.  I'd sniff the port briefly to check.  you can also use the exchange system manager to view current email connections and where they're coming from.
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Yaroslav_BuzkoCommented:
I'd also advise to carefully examine the headers of spam messages. What are the IPs of server it comes through? Please post a whole header here if the problem persists.

Chances are that some user at your LAN got some malware sending out spam and pretending to be 'external'.
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PsiCopCommented:
Also, realize that not all spammers pay attention to DNS. Some just sweep the 'Net looking for hosts that answer on Port 25 and then try to spam. So unless you've shut down your SMTP daemon, anyone who can connect to port 25 can send you E-Mail. DNS does not HAVE to be involved.
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knoxj81Commented:
Well to answer you question about what virus could do this, and what you can do about it. I would just run a scan @ www.trendmicro.com and see if anything comes up. If not, you know your barking up the wrong tree.
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SnodlanderCommented:
You may have an open relay on your exchange.
From an outside source see if you can telnet into your router on port 25 - post your results here
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