AS/Web modules are the first and the preferred way to go.
MPB messages are complementary to the usage of the AS/Web modules.
It is only in the absence of such AS/Web functionalities that some alternative is necessary.
And in such case, do not immediately fall back onto regular e-mail and the like, as these are no sound basis for automation on the recipient's side.
This "filter" is ment to guide you in using the MPB as the right alternative.
As the functionalities can vary per recipient (insurer) it is even possible to set up such preferences per insurer.
In such case, the generic and market-wide guidance is superseded by the guidance offered by that specific insurer.
In this stage things are filtered on the level of the Domains.
This might be too high a level.
AS/Web modules cover the scope of some policy-type or, often even more correctly said, of some (commercial) "product" (or some limited series of "products" or policy-types).
As a consequence, this filtering should allow the expression/guidance on that same (fine) level of policy-types and/or commercial "products".
(And yes, the term "product" is here to be understood as in the "PaF-tool" - the "Products and Formulas tool".)