On Tue, 12 Apr 2005, Danny Angus wrote:
Those who legitimately use outbound port 25 access
have alternatives already which include
<snip/>
asking your ISP for an exemption
If ISP's blocked port 25 and provided policed exemptions it would introduce
weak trust into an area where there is conspicuously no trust at all.
I don't see this as any more contentious than the blacklisting of ISP's
DHCP IP blocks, which stung some people at first but protected a whole lot
more in the long run.
Can you suggest a DNSBL that does this? We are using MAPS and Spamhaus,
but MAPS only lists a block if the ISP owning the block specifically
requests it, and Spamhaus seems to be very weak in this area also. For
example, we get several hundred messages from east.verizon.net every
day. Could there actually be legitimate MTAs in that block?
An advantage of using DNSBLs for blocking port 25 rather than having the
ISP do it at the router is that it is what economists call "incentive
compatible". That is, the work and expense (such as they are) are borne
by the individual/organization that benefits most. The benefit to the
source ISP is mostly a reduction in abuse mail - which many ISPs seem to
ignore anyway. The benefit to the receiving ISP is a reduction in inbound
spam, which is a big incentive.
Daniel Feenberg
d.
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