On Oct 24, 2011, at 9:29 PM, Dennis Burgess wrote:
I am curious about what network operators are doing with outbound SMTP traffic. In the past few weeks we have ran into over 10 providers, mostly local providers, which block outbound SMTP and require the users to go THOUGH their mail servers even though those servers are not responsible for the domains in question! I know other mail servers are blocking non-reversible mail, however, is this common? And more importantly, is this an acceptable practice?
It's both unacceptable in my opinion and common. There are even those misguided souls that will tell you it is best practice, though general agreement, even among them seems to be that only 25/tcp should be blocked and that 465 and 587 should not be blocked.
Most of our smaller ISPs that we support; we allow any outbound SMTP connection, however we do watch residential users for 5+ outbound SMTP connections at the same time. But if the ISP has their own mail
servers, and users wish to relay though them, we basically tell them to use their mail server that they contract with. What is the best practice?
Best practice is to do what works and block as much SPAM as possible without destroying the internet in the process. There are those who argue that blocking 25/tcp does not destroy the internet. By and large, they are the same ones who believe NAT was good for us. Owen