when a new email thread is created a message is added by core:

Others will only see this group after you sent a first message.

there is a new string in android (chat_unencrypted_explanation):

Messages in this chat use classic email and are not encrypted.

that should be used in the case of unencrypted chats, when they are created, and as the first message for incoming created groups (similar to what we do with "this chat is e2e encrypted" for encrypted chats)

(NOTE: for context see deltachat/deltachat-android#3926)