No, I think of another feature.
I am asking for monitoring (a list of) custom folders, in which mails are already stored (e.g. by sieve rules that sort them into the folder based on sender) and should be shown by Delta Chat.
It would be similar to monitoring the inbox, but using a custom list of folders instead of just the inbox.
Example:
Use-Case 1: Just DeltaChat
Monitor the DeltaChat folder. Possibly optimize messages for Deltachat, e.g., by stripping unnecessary headers and/or adding useful headers for sync between different DeltaChat clients.
Use-Case 2: Inbox + DeltaChat
Monitor Inbox, DeltaChat, possibly move messages from the inbox to DeltaChat.
When moving (i.e. having a “Chat Mode”), the mails can be changed, for example, to minimize overhead by stripping unnecessary headers, but it should be optional because one may want to retain the mails as they are so they can be treated like any other mail when using a mail program that is not DeltaChat.
Use-Case 3: Custom List (“Inbox”, “DeltaChat”, “Work”, “Family”) [don’t move, don’t change]
Monitor the folders “Inbox”, “DeltaChat”, “Work” and “Family” and show the conversations in DeltaChat. Don’t move the sorted mails but keep them in the corresponding folders as they are.