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How to find out which desktop is being used to send spam

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Last Modified: 2013-12-09
We are being blacklisted and our mail is getting rejected. Changing our outgoing ip gets the mail flowing again but after a while we get blacklisted again. Spam must be going out fron our location to cause this action. I installed wireshark to monitor the network traffic and capture packets. Is this the right software to use and what do I look for in the captured file?
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Commented:
Use your routers - Log all traffic going from your internal lan out through port 25.  Most likely you will see massive amounts of the same internal lan IP.
Another way to help would be to create a rule that only allows smtp outbound from IP XXX where XXX is your mail server

Author

Commented:
I have a Netopia R9120. Looked at the statistics and logs but there is nothing of value there. How can I create a rule to only allow outbound smtp from a prticular ip?

Commented:
not sure how to do it from the netopia but basically create a rule that says only allow smtp traffic (port 25) from 192.168.1.X to *

X = the internal email server
* is the wildcard to allow mail to get sent out.

Author

Commented:
Do you mean creating a rule for outbound smtp in the router?

Commented:
10-4

Author

Commented:
I have already done that. What I really need is to find a way to monitor port 25 to see which desktop is sending the spam.
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