A known chat contact uninstalled deltachat because the “empty” chat messages and return receipts in his MUA inbox annoyed him (his email provider only supports folders below the inbox). (EDIT: That issue causing this has been fixed in the meantime.)
Now I can not reach this contact anymore, because the last message received was encrypted from his former deltachat installation.
Some ways to control the encryption are needed. For example, it is also needed to allow reaching a known contact, and him to answer with a normal MUA, for example, once he gets into the office, after he left the phone with deltachat at home.
Force-once-unencrypted in Chat menu (when autocrypt is on, as if an unencrypted message had been received)
Force-once-encrypted in Chat menu (when autocrypt is off, as if an encrypted message has been received)
I would really like to be able to use encryption for some users and disable it for others… without having to go to settings every time and switching it on/off every time, of course a per-user setting
When I send an encrypted message to a contact who lost the private key, this message cannot be read. This situation usually occurs when this contact reinstalled/-configured Delta Chat, but cannot retrieve the former private key anymore, e.g. due to a former hardware failure followed by data loss.
I am thinking about something like this:
When such a contact has received my unreadable (encrypted) message, some kind of information like “You have received an encrypted message from [Name]. It cannot be decrypted because the appropriate key is missing. Shall the sender of this message be informed?” should appear. This way, the sender gets aware that the message cannot be read. (Because it is the first message to the sender after reinstallation/-configuration of Delta Chat has been done, it is unencrypted, but it contains the public key already.)
After the sender has been informed, her/his next step would be to import the new public encryption key for this recipient manually. The former key is declared to be invalid from this moment on.
Of course, I know that the approach of developing Delta Chat is that the user should be asked questions as less as possible, but I would not let do anything automatically in this case, as the reason of suddenly receiving an unencrypted message could be a third person who has hijacked the mail account of the recipient, too.
a per-user setting