Why your own emails land in spam: SPF, DKIM and DMARC explained simply

Mail providers like Gmail, Outlook, or GMX now automatically check whether an incoming email really comes from the domain shown as the sender. That check runs via DNS records on your own domain – if they're missing or misconfigured, even legitimate emails reliably end up in the spam folder or get rejected outright.

SPF: who's even allowed to send

SPF (Sender Policy Framework) uses a TXT record to define which mail servers are even allowed to send on behalf of the domain. If this record is missing or too restrictive, even legitimate mail servers – for example after switching providers – can suddenly be treated as unauthorised.

DKIM: a digital signature for every email

DKIM (DomainKeys Identified Mail) adds a cryptographic signature in the email header, verified via a public key stored in another DNS record – this reveals whether a message was altered in transit.

DMARC: the enforcing rule

DMARC (Domain-based Message Authentication, Reporting and Conformance) builds on SPF and DKIM and defines what should happen if a message fails one of those checks: do nothing, quarantine it (usually the spam folder), or reject it outright. A typical DMARC record starts with the tag v=DMARC1; followed by the desired policy, e.g. p=quarantine; or p=reject;, plus an optional reporting address.

Common pitfalls when switching providers

Whenever a hosting or email provider changes, these three records are, in our experience, the ones most often forgotten or copied incorrectly – for example when an old SPF record doesn't include the new mail server, or DKIM keys aren't regenerated during the move. A simple DNS check after every provider switch usually catches these gaps reliably.

Our take: on every project where we set up DNS and mail delivery, we specifically check SPF, DKIM, and DMARC – an email sitting in spam ultimately reaches no one.

Sandro Geissmann | Geissmann Webconsulting

All articles are general professional background information and do not replace individual legal or professional advice.