How Speaking Email handles reply and forward conversation threading
We treat conversation threads a bit differently, it's not like Gmail for example where you can expand and collapse the replies in the thread because we are preparing the content as speech.
We automatically scan for your email address and stop reading out the email at the point that we know it already was sent to or from you. This way Speaking Email reads right to the point it needs to. If we simply cut off at the first reply we might miss something - for example if someone forwards you an email you don't just want to hear that person's words "see below - unbelievable". If we combined all replies from a thread together in one screen, we might be reading out old messages that you've seen before.
If you don't have this feature switched on, its under Preferences.
PS. If you want Speaking Email to keep going beyond the thread cut off, you can just say "continue" to have it do so.