ISP port blocking practice

James R. Cutler james.cutler at
Fri Oct 23 23:33:58 UTC 2009

No, blocking a port does not restrict a customers use of the network  
any more than one way streets restrict access to downtown stores. It  
just forces certain traffic directions in a bicycle/motorcycle/car/van/ 
truck neutral manner. Carry anything you want.  Others laws restrict  
incendiary content.

On Oct 23, 2009, at 6:15 PM, Dan White wrote:

> On 23/10/09 17:58 -0400, James R. Cutler wrote:
>> Blocking the well known port 25 does not block sending of mail. Or  
>> the
>> message content.
> It does block incoming SMTP traffic on that well known port.
>> I think the relevant neutrality principle is that traffic is not  
>> blocked
>> by content.
> My personal definition doesn't quite gel with that. You're deciding  
> for the
> customer how they can use their connection, before you have any  
> evidence of
> nefarious activity.
> Would you consider restricting a customer's outgoing port 25 traffic  
> to a
> specific mail server a step over the net neutrality line?
> -- 
> Dan White

James R. Cutler
james.cutler at

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