Yakov Shafranovich wrote:
So what comes out from this, is that SMTP operates on a hop-by-hop
basis, which in many cases is end-to-end since there is only a single
hop to be done.
Now the question is, what can we, as a RG, learn from this? How is this
behavior helpful to stopping spam? What comparisons can we draw from
this behavior to other protocols?
IMHO there is an email network built over the IP network. The email
network is comparable to the IP network.
Routers are hop-by-hop devices on the IP network while MTAs are
hop-by-hop devices on the email network.
IP numbers and mailbox addresses can not be owned they must licencing.
IP numbers and mailbox addresses are (like) licence IDs.
IP routers can enforce licencing (can stop IP spoofing) because the
communication paths related to the forward licensing structure of the IP
numbers.
MTAs can not enforce licencing (email address forgery).
A host do forward licencing of IP number(s) to its services. A TCP
service do forward licencing of port access to clients during the
handshake while UDP does not. The port number and the sequence number
are (like) licence IDs.
TCP can enforce the licencing because the sequence number is related to
the sender and the licence number must be attached to each message.
Additionaly sequence numbers are unpredictable by third parties.
Back to Your question:
> How is this behavior helpful to stopping spam?
I dont know about spam-like traffic on the TCP network except port
scanning, SYN flood and IP spoofing. They are comparable to dictionary
attack, C/R attack and email address forgery on the email network.
Port scanning can be handled by log analysis, SYN flood attacks can be
handled by cookies, and IP spoofing can be handled by exchanging
unpredictable sequence numbers during a handshake procedure.
So organizing communication paths between MTAs closer to the forward
licencing tree (as in the case on the IP network) and/or forward
licencing mailbox resources to senders during handshake procedures will
help enforcing sender licecing on the sender side and/or at the
receiving side.
IMHO enforcing licences may significantly decrase delivery of (today) spam.
And back to the subject:
Spam is exist in SMTP because the communication paths of the email
network does not related to an enforcable forward licencing structure
and because senders can reserving resource from the receiver without
licence.
z2
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