Fixes, not fluff. DNS security and compliance guides for IT managers who already know the acronyms.
When DMARC alignment fails but SPF passes, your envelope-from or DKIM domain does not match the visible sender. Quick diagnosis from Authentication-Results and ESP fix steps.
When SPF passes but mail lands in spam, DMARC alignment, missing DKIM, or envelope-from mismatch is the usual cause. Diagnosis and fix steps for Gmail, M365, and ESP relay sends.
The 550 5.7.26 authentication required bounce means Gmail rejected your message before inbox placement. Fix SPF, DKIM, DMARC alignment, and envelope-from settings for M365 and Google Workspace.
Gmail and Microsoft spam-folder legitimate mail for authentication, DNS, reputation, and list-hygiene reasons most admins never audit. All 35 failure modes and fixes in one guide.
New DNS advisories, monthly. What broke, who it hit, and the record that fixes it.
