Email authentication guides
Practical, no-nonsense guides to SPF, DKIM and DMARC. Fix what is broken and keep your mail out of spam.
Multiple DKIM Selectors on One Domain: Signing for Google, SendGrid, Mailchimp and More
DKIM is designed for many keys on one domain. Each sending service publishes its own public key under a unique selector, so Google, SendGrid, Mailchimp and every other stream can sign mail independently. This guide maps the common selector conventions per provider, explains the one rule you cannot break, and shows how to verify every stream.
DKIM Fails but SPF Passes: Why It Happens and How to Fix the Signature
When DKIM fails but SPF passes, the sending IP was authorized but the signature broke. This guide diagnoses the signature-level causes: body hash mismatch from list footers and forwarding, altered headers, missing selectors, truncated keys, and l= body-length quirks. Includes a symptom-to-cause table, a step-by-step verification loop, and how signature failures differ from DMARC alignment failures so you fix the right thing.
How to Read the Authentication-Results Header: Decode SPF, DKIM and DMARC
The Authentication-Results header is your receiving mail server's verdict on whether SPF, DKIM and DMARC passed. This guide annotates real headers from Gmail, Outlook and Yahoo field by field, gives a lookup table for every result value from pass to permerror, explains smtp.mailfrom, header.i and dis=, and ends with an if-X-failed-fix-Y decision tree so you can turn a confusing string into a fix.
Why Your Emails Go to Spam
When mail lands in spam, the first suspect is authentication, not content. Here are the SPF, DKIM and DMARC reasons and how to fix each one.
Google and Yahoo Sender Requirements
Since 2024, Google and Yahoo require senders to authenticate their mail. Here is what the rules actually ask for and how to comply.
SPF, DKIM and DMARC for Microsoft 365
Microsoft 365 sends your mail but does not authenticate your domain for you. Here are the exact SPF, DKIM and DMARC records to publish.
How to Fix the SPF Too Many DNS Lookups Error
SPF fails with a permerror once your record needs more than ten DNS lookups. Here is why it happens and three reliable ways to get back under the limit.