Sending works, nothing comes in, and no bounce shows up anywhere. That asymmetry tells you almost everything: inbound mail is decided by MX records, not by SPF. This guide walks the inbound path in the order a sending server actually walks it, groups the real causes into five DNS failure families, and gives you the dig commands to prove which one you are looking at.
Moving one WordPress site is easy. Moving twenty in a weekend is a pipeline, and the failures that cost you are the quiet ones: writes landing on the old server, cron firing on two boxes, certificates blocked by ACME rate limits. Here is the fleet migration process I use, from manifest to per-site rollback.
The rule went red at 02:04 and nobody found out until 09:15. Rule evaluation and notification delivery are two different systems, and only one of them is visible in the UI. A practical setup for Grafana alert notifications to email, Slack and Telegram, plus how to detect the day delivery quietly stops.
Your domain has all four records. Every free checker shows green. It is still trivially spoofable, because publishing a record and enforcing a policy are different acts. A working guide to business email DNS: what MX, SPF, DKIM and DMARC each actually protect, the SPF lookup budget and the void-lookup limit nobody watches, why DKIM alignment decides whether you can ever reach p=reject, the domain architecture that stops the problem recurring, and a rollout order that gets you to enforcement without losing legitimate mail.
Migrations rarely fail loudly. The site stays up while mail, cron, certificate renewal and the write path break silently behind it. A post-migration checklist for the first 48 hours, ordered by how long each failure can hide rather than by subsystem.
WordPress tells you the mail was sent. The customer never got it. This is a working guide to the four places WordPress email deliverability actually breaks: PHP mail() transport, SPF lookup limits, DKIM alignment, and DMARC policy. Includes real diagnostic commands, a troubleshooting order, and what changed now that DMARC has moved onto the IETF standards track.