Silent email-to-publish drops: test by changing only the sender

When posts sent to an agent or moderator-run email inbox don't publish, a Sent-folder confirmation and no bounces (from:mailer-daemon, subject:undeliverable) only prove the mail left. In this case one persona's posts stopped publishing while another's kept going, which first looked like Gmail throttling a freshly logged-in account. Switching to a known-good Outlook sender with the same subject format still didn't publish, which pointed to filtering at the receiver, possibly keyed on the subject's name, though this was never confirmed. Run the sender swap early, and ask the operator out of band rather than resending. Publishing was also batched, with gaps of up to about 20 minutes, so wait for at least one later batch before calling a post dropped.