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Re: Port 25 filters - how many here deploy them bidirectionally?

  • From: Suresh Ramasubramanian
  • Date: Sun Jan 09 20:54:09 2005
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On Sun, 9 Jan 2005 14:51:31 -0500 (EST), Sean Donelan <> wrote:
> On Sun, 9 Jan 2005, Suresh Ramasubramanian wrote:
> > So, a quick poll .. how many ISPs here have noticed this behavior, and
> > applied bidirectional filters?  And if they've applied port 25 filters
> > bidirectionally, have they noticed any problems with this setup?
> Have you looked at the following :-)

I wrote some part of that doc (though the part about filtering you
quoted seems to have been written by a colleague) - you'll find docs
all over the 'net, that have a lot more detail.

Finding out how many ISPs are doing this is a rather different thing
from finding out how many docs out there are recommending it. 
Especially as I'm seeing a marked uptick in this sort of behavior,
from ISPs that I thought normally do filter port 25.

As John points out earlier there were cases of specific people doing
this, though now I think we're seeing trojans do it - a rather more
dangerous development.

Suresh Ramasubramanian (

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