Email authentication becomes easier to reason about when each mechanism has one clear job. SPF, DKIM and DMARC are related, but a green result for one is not a substitute for the others. They also do not measure whether a reader wanted the message.
SPF identifies authorised sending infrastructure
SPF is published in DNS and describes which systems may send for an envelope domain. During setup, follow the exact provider instructions and account for other legitimate senders. Avoid improvising a second independent SPF policy at the same hostname when updating an existing configuration.
A common debugging mistake is looking only at the visible From address. The identity evaluated by SPF is not simply that display field. Inspect the message's authentication results when investigating a real delivery problem.
DKIM provides a verifiable signature
DKIM adds a signature to a message that a receiver can verify using a public key in DNS. The selector identifies which key to look up. This is why a DKIM checker asks for more than the domain name.
Use Sendar's generated DNS values for your sending domain. A published key under a different selector does not demonstrate that the signature on your message validates. Where possible, examine the received message as well as the DNS configuration.
DMARC adds alignment and policy
DMARC connects authentication results to the domain in the visible From address through alignment. It also lets domain owners publish policy and reporting preferences. Moving to an enforcement policy should follow an inventory of legitimate sending services, so expected mail is not accidentally disrupted.
Google's sender guidance distinguishes requirements for all senders from additional requirements for high-volume senders to personal Gmail accounts. Consult the current guidance for the traffic you send rather than assuming one checklist fits every recipient system.
Use diagnostics for the question they answer
Sendar's public checker shows DNS observations. It does not expand every SPF include, evaluate DMARC parent inheritance or guarantee inbox placement. Treat its result as one piece of evidence. A complete investigation also considers the actual message, recipient responses, sending history and whether the audience expected the email.