Better folder navigation with long lists and hierarchies

[IMSoP]

Checklist

• [X] I have used the search function to see if someone else has already submitted the same feature request.
• [X] I will describe the problem with as much detail as possible.
• [X] This issue only contains a request for one single feature, not multiple (related) features.

App version

8.0

Problem you are trying to solve

I like to organise my mail into a large set of IMAP folders, and use nested folders to group them. This works very nicely in many clients, including Thunderbird for desktop, where I can collapse sections of the tree for easier navigation.

K-9 Mail has never supported the nesting explicitly, but shows each folder separately as "Foo/Bar", meaning more scrolling.

The new folder navigation in 8.0 makes this much, much worse, because of the increased padding around the names.

On my Nokia 5.4 (a reasonably standard sized screen), there is room for 14 items at the new spacing; 3 of these are fixed (the account header, "Manage folders", and "Hide accounts"); the first screen is almost entirely taken up by default IMAP folders, then I have to scroll to see at most 11 folders at a time.

Suggested solution

Firstly, some options for the padding:

• Reduce the default padding; space is at a premium on small screens.
• Add a "Density" setting for the Folder List, similar to the one for the Message List.
• Automatically adjust padding based on number of folders.

In addition:

• Show nested folders as a tree / accordion. For instance, a + / - button or rotating arrow to the right of a folder name could show/hide all folders nested inside it.
• Ideally, the state should be remembered when closing and opening the app, so that rarely viewed sections could be collapsed and opened only when needed.

Screenshots / Drawings / Technical details

No response

[IMSoP]

Note that this was also raised on the K-9 forum here: https://forum.k9mail.app/t/compact-folder-list/10701

It would be helpful if a member of the development team replies there, linking to this issue if you agree it is something you can look into

[IMSoP]

Here's a screenshot. This would be fine if I used only or mostly the Unified Inbox + 7 standard IMAP folders at the top, but only 3 of my long list of custom folders now fit on the first page.

[rezazarchi]

This issue seems related to #630 or duplicated, but your description is much more detailed and can be helpful for doing that.