Authentication broke
01 / 05Somebody touched the DNS. A domain moved, a record expired, an IT ticket closed without anyone telling marketing. Inbox providers check your domain rules (SPF, DKIM, DMARC) before they trust a word you say. When one breaks, everything you send after it pays for it.
Tell-tale signs it started on an exact date. Bounce messages mention authentication or “unauthenticated.” Something changed recently: a new domain, a new tool, a website migration.