How to pass an argument to be used in the view called by rules
I found 2 working prototypes.
Each require a taxonomy-list "field of interest" in both user and node.

Users can select multiple items, according to their fields of interest.
When registering a new post, the posting user can indicate in which field of interest (one) this post is matching.

ONE

using 5 views (one for each term) to select the email adresses of users interested in this "field of interest".
In the action I use "switch case" (from conditional_rules) to select the view corresponding to taxonomy-term of the new node

TWO

fetch entity (user) by taxonomy term(field of interest)

loop thru the list of users

THREE

Finally I chose to make 5 views and 5 reaction rules, each rule having as condition a particular value of the taxonomie term in the new node en using the relevant view to select the users. No switch case needed.