How can I tell which computers are sending SMTP email out of my network?

I manage a network of 10 PC's. We have been recently blocked from sending emails to a few domains. Afer performing a full and thorough virus scan on my computers and server, we still seem to be blocked. Is there a tool (free preferably) that i can set up to only allow SMTP traffic to originate from my email server?

How can I tell which computers are sending SMTP email out of my network?systemworks

your network will have a router or a firewall ( or both ) that will allow you to set up access list - you need to set up a filter that only allows your email server to send smtp traffic - ( all other devices will get their email from this server ) - also worth making sure that your server isnt configured as an smtp open relay .. as it could be used by spamers to relay messages and may be the reason your are being blacklisted ( you need to ensure that youre mail server only forwards email from addresses on your network - or that have been authenticated ) search for open relays or spaming

How can I tell which computers are sending SMTP email out of my network?windows

From what you have said I do not think that a virus is your problem. You say that you manage a network of 10 pcs? Did you inform your ISP of this as it could be against your contract?

This may be the reason that port 25 has been blocked.

If you want to run servers, then you may need to upgrade to business account, where there are no such blocks.

Sorry for not being able to offer a quick fix!

In the meantime you can download a Network Traffic Monitor from http://www.tucows.com/preview/418063. It is shareware so it is free.