Hi there,
We had Google Groups forward to Zendesk but unfortunately some emails that we didn't intend to filter were filtered and suspended. Since notifications weren't sent to us/customer, we weren't aware of this for some time, and many of those emails were auto-deleted.
We hoped we could recover most of these, but currently suspended tickets are deleted after two weeks. Given tickets are usually short pieces of text, don't see why they can't just be marked as archived and kept around for longer just in case.