Blocking MX query

Michael Thomas mike at
Tue Sep 4 16:59:07 UTC 2012

On 09/04/2012 05:05 AM, William Herrin wrote:
> There are no "good" subscribers trying to send email direct to a
> remote port 25 from behind a NAT. The "good" subscribers are either
> using your local smart host or they're using TCP port 587 on their
> remote mail server. You may safely block outbound TCP with a
> destination of port 25 from behind your NAT without harming reasonable
> use of your network.

Would that were true going forward. Consider a world where your
home is chock full of purpose built devices, most likely with an
embedded web browser for configuration where you have a
username/password for each. In the web world this works because
there is a hidden assumption that you can use email for user/password
reset/recovery and that it works well. When your boxen can't do that
because email is blocked, what are you going to do? Reset to factory
defaults? Every time I forget? And please lets not get another useless
lecture on why the unwashed masses should be using password vaults.
They won't.

This hidden assumption of a reliable out of band mechanism for account
recovery is going to come to the fore as v6 rolls out and ip is as gratuitously
added to cheap devices as digital controls are now. Email is the glue that
keeps the web world functioning. Until there's something else, it will
continue to be needed and its role will expand in the home too.


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