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Hi Ronald, here it comes, my suggestion for the ISP. Put all your dynamic IP addresses on the available blacklists right away to support the SPF! Who in earth is using a dynamic IP to set-up a viable MTA services on that? I would encourage any company to use their public MTA with a service provider doing this for a living. How do you get a proper reverse DNS entry for a dynamic IP? (Yet another technique to evaluate the sender). Seriously, I can provide logs of our anti-spam servers ranging back to 2 years. The amount of servers or companies setting up there email server on a dynamic IP is little because it doesn't make sense. The only workaround to the SPF dilemma would be to use a dynamic DNS service and even then, every time you login you might get assigned an IP which is listed on a blacklist. Also, I can send an email via port 25 and it won't show my public IP as the sender address. This is because I am submitting to the MSA which forwards to the MTA and the MTA's IP would be the one shown as the sender. (double function of port 25). You could send to the receiver's server directly using the email client as a MTA (not recommended) or you use a MSA in the middle. E.g. if you have an internal email server (MTA/MSA) it can be configured to forward the messages to the MSA of an email provider (called smart host) despite of being a MTA internally. You can see all the different stages of the email delivery and the different MTAs the email has gone through in the email header, but the last entry is the most important one. So, back to the question: port blocking on port 25 vs usability for MUAs using MSAs on port 25 vs achievements of the block to reduce spam. There are a number of comments and articles in the net saying that it has helped a lot. Since I don't have access to traffic logs of ISPs and I can't find any figures or reports supporting the achievements, I can only use our own antispam server logs to come to a conclusion. Which is that it doesn't make a difference if a spam comes from a dynamic IP of an ISP's IP pool or from a static IP of a compromised server. I personally don't suggest anyone to use port 25 or port 587 for mail submission. I have pointed out the issue with security vs TLS in a post earlier. Regards, Rocco On 2010-02-10 18:52, Muwonge Ronald wrote: Hi Rocco |
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