Hello Proton Team,
First of all, as a French user, please excuse my English which might leave a little to be desired... ;)
Thank you for your excellent work. As a daily user of your services, I would like to share two feature suggestions regarding the Proton Mail interface that I believe would greatly improve the overall user experience:

Increase the subfolder limit: Being a true neat freak when it comes to organization, I find the current 3-level hierarchy limit a bit restrictive. It would be incredibly useful to be able to create more nesting levels for hyper-precise categorization (this is especially helpful when relying on advanced automated sorting filters).

Notification badge on collapsed folders: When a parent folder is collapsed, it would be perfect to have a visual indicator (like a small dot or badge) showing that one of its hidden subfolders contains unread emails. Currently, we have to expand the whole tree just to check if we missed anything.
Thank you for considering this feedback for your future updates!
Best regards,