Hallam-Baker, Phillip wrote:
Layers are tools for design, as well as analysis. Collapsing layers
requires very, very careful attention to the implications.
When you are dealling with a twenty year old protocol you are likely
to find that the reason it is failing is that the original layering
design was inappropriate for current uses.
I am not sure this is true in this case. The problem is one of trust and
it has nothing to do with layers. If we have a system in place to
somehow exchange trust information about MTAs there is no reason to mix
This is why I think that HELO checking might be sufficient. Many people
have already stated that MAIL FROM without a reputation/accreditation
hook is useless. A HELO mechanism would provide such hook without a need
to some of the more painful changes involved with MAIL FROM and RFC2822
checking. Once you establish trust of a given MTA, than you can trust it
to supply you with non-forged information.