Email Categories can currently only be influenced by manually moving messages and waiting for the model to learn. For some senders this never converges. For example, Substack newsletters are consistently put in the wrong category for me, even after repeatedly moving them to Newsletters. Users need a deterministic override.
Please add:
1. A "Move to category" action in custom filters, and a Sieve equivalent (e.g. setcategory "Newsletters";).
2. An "Always categorize this sender as ..." option, like the existing "Always move sender's emails" checkbox, ideally also at domain level (e.g. *@substack.com).
3. Clear precedence: explicit user rules override automatic categorization.

This would also cover the related request to set categories based on the receiving alias (https://protonmail.uservoice.com/forums/284483-proton-mail-calendar/suggestions/51648520-category-based-on-e-mail-alias), since the alias could simply be a filter condition.