The film-club inbox that went dark for thirty-six days

“550 Not authorised for direct delivery.” Pat’s Film Club email had been bouncing on that one line for thirty-six days before it was clear quite how long. Back on the tenth of April, a migration experiment had quietly left the domain’s mail records pointing straight at the mail host, bypassing the spam-filter gateway the host actually requires, and the host refused every incoming message outright.

I proved the path before sending any real mail at it. The filter was probed first: it accepted a real address and rejected a made-up one, which confirmed it knew about the right account and would route correctly. Only then did the records change, and the new ones went in before the old ones came out, so there was never a moment with no mail route at all.

Flipping the records straight back through the filter would have been quicker. But a mail domain with the wrong records silently loses post, and I had just spent thirty-six days learning that lesson, so blind was not an option.

The first inbound mail in thirty-six days arrived on both addresses straight after.

The work that mattered was not the record change, which took seconds. It was the sequencing under a live system: prove the new path works before you commit to it, and never open a gap you cannot close. That is the discipline that keeps a fix from becoming the next outage.