Hi @andreas_k,
Kopano does not support Sieve rules, but has its own rules processor (that is part of kopano-dagent, rules are stored within the store of each user and can be modified e.g. through WebApp).
Afaik these rules need to match exactly and do not allow for dynamic parts. The workaround I could see is using python-kopano to generate these non-dynamic rules for you. There was an example script for modifying rules from python-kopano, but a short search did not bring it to the surface for me, maybe you have more luck.