David Maxwell <david(_at_)crlf(_dot_)net> wrote:
One question I have about MTAMark - how does its effect differ from the
effect of blocking outbound port 25 (other than from authorized MTAs)?
Source filtering is more network friendly than recipient filtering.
In one way, port blocking is better, since it requires no implementation
on the recipient's side. However, MTAMark would give the recipient the
responsibility for the consent decision.
The benefit of port blocking is that it makes a local network
responsible for it's own behaviour. The problem is that there are
currently few options deployed to work around port blocking. (SUBMIT?
Who uses that?)
The benefit of MTAMark is that it allows roaming users to continue
to use 10-year old protocols and behaviours, so long as the recipient
chooses to ignore MTAMark. This works if the recipient can
authenticate the roaming user.
The problem of MTAMark is that it pushes responsibility for the
traffic onto the recipient. Broken senders can still flood the
network with garbage, so long as the recipient is smart enough to
throw it away.
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