Inventory every sender
List employee email, website forms, invoicing, customer-management tools, newsletters, and transactional applications. Record the owner and sending domain for each.
Ask whether each system is still used and how a delivery problem is reported. An unused integration can be removed deliberately after its owner confirms it is no longer needed.
Check authentication
Confirm SPF and DKIM for the actual sending services, then review DMARC alignment. DMARC can pass through aligned SPF or aligned DKIM, as described in Google’s sender requirements.
Use message headers and provider tools to test actual mail. A DNS record existing is not the same as every sending system using it correctly.
Review subscriptions and suppression
Confirm that recipients requested the mail and that unsubscribes are honored. Google specifies additional one-click unsubscribe requirements for certain bulk marketing and subscribed mail in its sender guidance.
Check how bounced, complained-about, and unsubscribed addresses are handled. Avoid restoring suppressed contacts through an import without understanding why they were suppressed.
Inspect messages and errors
Test representative messages, links, sender names, and reply handling. Review bounce and deferral messages with the provider responsible for the send.
Separate a provider accepting a message from the recipient seeing it in the inbox. Authentication and successful submission alone do not establish inbox placement.
Change one thing deliberately
Document the current state, the proposed correction, and the expected evidence of improvement. Avoid sudden sending-volume changes while diagnosing a problem.
Keep a record of the change and monitor the same types of messages afterward. Escalate with example headers and error responses rather than a general report that email is broken.