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Re: Fixing graylisting [was TBR]

2007-11-15 13:35:12

On Nov 15, 2007, at 11:41 AM, SM wrote:

At 10:02 15-11-2007, Douglas Otis wrote:
The TBR extension can:

1) without burdening the receiver

a- provide a valid identity of origination

b- eliminate back-scatter

It may eliminate backscatter but it introduces a new problem, i.e. it can be used to stage attacks using HTTP.

Only to HTTP servers located within the "_tbr." subdomain. This will not impact other websites. In addition, fairly straight forward anti- abuse measures can be applied, and are recommended in the draft.

5) protect valid email-address confidentiality

See Section 7.6 of RFC 2821 about information disclosure in message forwarding.

This was not the concern. An attempt to send to an invalid recipient is likely to return an error which may indicate their non-existence. Dropping any acknowledged message will have the effect of lowering email's delivery integrity. For those messages being handled by incoming filtering services, RFC8221 section 4.2.5 Reply Codes After DATA and the Subsequent <CRLF>.<CRLF> requires either the message be delivered, or a DSN be made. These services will either produce a flurry of backscatter, cause messages to be lost, or permit valid recipient addresses to be discovered. The TBR extensions is better able to obfuscate whether a message was refused due an opinion of the origination, or due to an invalid recipient. Seeing a series of invalid recipients would be a clear indication of this being abusive. Any lucking guesses can be expunged when a short hold is placed upon suspicious points of origination.