Provide a way to clear downloaded attachments

Checklist

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

App version

6.603

Problem you are trying to solve

Reduce app size (cache).

Suggested solution

Apps like Whatsapp provide a UI for managing file storage (sorted by size, date, sender etc).

Currently for K-9, you can only clear the entire cache. There is no way to remove individual attachments/images. I only need a few attachments on my phone beyond initial viewing. The rest are just taking space and it is enough to keep them on the server.

Please note that I am not talking about attachments saved by tapping on the download icon which invokes the SAF.

Thank you

Screenshots / Drawings / Technical details

No response

The issue names no files, tests, or entry points. Start by locating the attachment cache and the existing full-cache clearing UI; done should provide a way to identify and remove individual cached attachments while keeping server copies, without affecting files saved through SAF.