North American Network Operators Group

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Re: SMTP Port Blocking: Success or Failure?

  • From: Jason Nealis
  • Date: Mon Feb 28 13:26:40 2005

We put our blocks in place some time ago, Mainly on the Cable Modem side. We found
our userbase was very prone to becoming zombie agents for spam.  We did
enhance our static i.p product by allowing statics to have port 25 open, this
averted any real business class customers to continue to function. 

The benifiet was seen pretty quick here,  That in combination with 
some throttles permiting the standard customer only to send 400emails 
in a hour has cleaned us up pretty significantly. 


On Sat, Feb 26, 2005 at 07:04:26PM -0600, Claydon, Tom stated
> We are considering filtering outbound SMTP traffic from our ISP
> customers, except from our own mail servers, to help reduce the amount
> of spam originating from our network. How successful/unsucessful has
> implementing outbound SMTP filtering done in stopping or slowing down
> spam from your network?
> Also, if outbound SMTP filtering has not worked for you, are there any
> other things that you have implemented that have helped with spam
> traffic?
> Thanks,
> = TC
> --
> Tom Claydon, IT/ATM Network Engineer
> Dobson Telephone Company


Jason Nealis
Internet Systems and Services