North American Network Operators Group

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Re: ingress SMTP

  • From: Simon Waters
  • Date: Fri Sep 05 04:22:16 2008

On Friday 05 September 2008 00:33:54 Mark Foster wrote:
> *rest snipped*
> Is the above described limitation a common occurrance in the
> world-at-large?

If the ISP blocks port 25, then the ISP is taking responsibility for 
delivering all email sent by a user, and they have to start applying rate 
limits. Otherwise if they send all email from their users, all they've done 
is take the spam, and mix it in with the legitimate email, making spam 
filtering harder.

Locally one of the big ISP insists you register all sender addresses with 
them, so all the spam from them has legitimate sender credentials.

The problem is that by blocking port 25, you are basically then switching 
users to arbitrary per ISP rules for how to send email. This is probably good 
for ISPs (provides some sort of lock-in) but bad for their users.

Whilst the antispam folk think it is a godsend because their block lists are 
smaller, it is relatively easy to block spewing IP addresses, and hard to 
filter when good and bad email is combined. Which is why they hate Google 
hiding the source IP address.

This will continue until the real issue is addressed, which is the security of 
end user systems.