Currently in the desktop website and Windows application (and likely more), Proton Mail's process for adding to the spam/block/allow lists involves:

1) Clicking the 'Add address or domain' button.
2) In the opened dropdown, selecting which list to add to.
3) In the opened pop-up, selecting whether to add an email or domain, and providing the email/domain to add.

This is not optimal, since:

1) The contents of the pop-up are functionally identical regardless of the selected list in the dropdown, so the pop-up has no reason to appear only after the list selection has occurred.
2) If needing to add a large number of emails and/or domains at once, the pop-up appearing and disappearing every time can slow users down. Particularly due to its different placement to the 'Add address or domain' button, requiring users to frequently move their cursor back and forth between the button and pop-up.

As such, the UI for adding to these lists should be changed for a better user experience. I personally think the UI should either be entirely confined to the pop-up (i.e. multiple emails/domains can be added without leaving the pop-up), or should remove the pop-up as a whole. Though any alteration which addresses these issues is welcome.