Outgoing SMTP Servers

Bjørn Mork bjorn at mork.no
Tue Oct 25 12:43:56 UTC 2011

Owen DeLong <owen at delong.com> writes:

> It's both unacceptable in my opinion and common. There are even those
> misguided souls that will tell you it is best practice, though general agreement,
> even among them seems to be that only 25/tcp should be blocked and that
> 465 and 587 should not be blocked.

It is definitely considered best practice in some areas.  See e.g.
(couldn't find an english original, but the google translation looks OK)

The document is signed by all major ISPs in Norway as well as the
Norwegian research and education network operator, so it must be
considered a local "best practice" whether you like it or not.

Note that only port 25/tcp is blocked and that some of the ISPs offer a
per-subscriber optout.

Eh, this was the Northern Aurope NOG, wasn't it?


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