Conversation threading should be a per-folder setting
Conversation threading should be a per-folder setting, so, for example, my Inbox could have it on and my Sent Mail could have it off.
should be included the email deleted
MICHAEL CACCIATORE commented
Should be able to list all/partial folder (conversation threading folder settings).
In this case should be possible for someone to have the "conversation" including the mail deleted+sent+inbox (full conversation) or selected folders for someone else (as for ex. only inbox and sent). Today is only sent+inbox but hardly to manage when you receive