Here is a situation.
Lets say an IP address is blacklisted on the internet due to the spread of Trojan. Lets assume IP addresses here. Customer is running an email server and the IP is 1.2.3.4. There is a trojan on this network which is spreading out spams . When I search for this IP in dnsstuff.com , I see that multiple websites have blacklisted the IP 1.2.3.4 . The DNS server is also running on 1.2.3.4.
Lets say I move those email accounts to a different email server(2.3.4.5).. If they now send an email from their network , their email header would say
mail from 2.3.4.5 <== Email server
originating IP : 1.2.3.4 <== Their network..
Since 1.2.3.4 is already blacklisted on the internet , would they be able to send emails atall as the receiving email server would reject those if they have use DNSBL lists or they should have no issues as the receiving mail server would only care from which email server the email is coming through and not the network..
personally , I would not move the email accounts until the trojan is removed from the network but this is a curious question that got me thinking..
SR
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by: johnburnettPosted on 2005-10-11 at 16:30:50ID: 15065366
The blacklists go by the IP address of the originating SMTP connection on Port 25. They're not at all concerned about what the email header says - any script kiddy can forge an SMTP header. So no, they won't be able to send email from any email host on that network unless that host is statically NATted to a second public IP other than 1.2.3.4.
Nor should they. It's grossly irresponsible to connect ANY email host to the Internet from a network where a trojan is suspected of residing.