Postalfix

An SPF (Sender Policy Framework) record is a DNS TXT record that lists which mail servers are authorized to send email on behalf of your domain. It helps prevent email spoofing and improves deliverability by telling receiving servers which sources to trust.

DKIM (DomainKeys Identified Mail) adds a cryptographic signature to every outgoing email. Receiving servers can verify this signature against your public DKIM key published in DNS, proving the email was not tampered with and truly came from your domain.

If your IP or domain appears on a blacklist (RBL), major email providers like Gmail and Outlook may reject or flag your emails as spam. Use our blacklist checker to identify listings early and follow the delisting process for each RBL provider.

Reverse DNS maps your server's IP address back to its hostname. Many mail servers reject emails from IPs without a valid PTR record because it is a strong indicator of a properly configured, legitimate mail server. Always ensure your PTR matches your sending domain.

DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM to tell email receivers how to handle messages that fail authentication. It also provides reports so you can monitor who is sending email on behalf of your domain. Every domain that sends email should have a DMARC record.

DNS changes typically propagate within a few minutes to 48 hours, depending on the TTL (Time To Live) value of your DNS records and how quickly different DNS resolvers refresh their cache. Lowering the TTL before making changes can speed up propagation.

SPF specifies which servers are allowed to send email for your domain, while DKIM cryptographically signs each email to prove it was not altered and truly came from your domain. Both are complementary: SPF verifies the source, DKIM verifies the message integrity.

Common causes include missing or incorrect SPF, DKIM, and DMARC records, a blacklisted IP address, poor sender reputation, low engagement rates, and spammy content. Use Postalfix to audit your DNS records and blacklist status to identify the root cause.