My email was bouncing, and perhaps coincidentally with a DNS message similar to the one gnarlymarley pasted for gmail. Cleared the error and now submissions work normally.
Earlier this morning my submissions were working normally, but any submissions made after that return nothing. I'd like to verify that my reporting address is okay, or perhaps there are other issues with my submissions. It's hard to tell with no response at all. Is there an outage or other problem with the reporting system?