support.google.com/a/answer/2466563?hl=en

Once SPF and DKIM are in place, you configure DMARC by adding policies to your domain's DNS records in the form of TXT records (just like with SPF or ADSP).

dkimcore.org

DKIM Core is a way to attach a token (or tokens) to an email that tells the recipient who is responsible for the email (typically the token would represent the author of the email, the operator of the email service, or the owner of a mailing list, but ...

vamsoft.com/support/tools/spf-syntax-validator

Helps creating SPF policies by validating the syntax of SPF policy data.

vamsoft.com/support/tools/spf-policy-tester

Test IP addresses against live or a directly entered SPF policy and get a detailed evaluation log of the test. Helps with troubleshooting.

otalliance.org/resources/spf-dmarc-record-validator

Tool to validate if SPF and DMARC records have been "published" in a domain's DNS zone file. The tool will query the DNS of the respective domains and present the records found. Up to 500 domains may be entered. Tools to validate SPF and DMARC records ...

www.seoconsultants.com/tools/spf/

What is SPF? SPF fights return-path address forgery and makes it easier to identify spoofs. Domain owners identify sending mail servers in DNS. SMTP receivers verify the envelope sender address against this information, and can distinguish authentic me ...

www.spfwizard.net

This ajax enabled wizard will guide you through the process of creating or editing a SPF record for your DNS domain. You should add this DNS record to your domain's DNS configuration.

www.spfwizard.net/what-is-spf-record.html

An article on what Sender Policy Framework (SPF) is.

www.openspf.org

The homepage of the Sender Policy Framework project.

dkimvalidator.com

Now you can quickly view your DomainKeys, DKIM, and SPF validity, and SpamAssassin score in one place. Just send an email to any address @dkimvalidator.com. Then check here to see the results.

www.protodave.com/tools/dkim-key-checker/

Use this tool to lookup and verify a DKIM TXT record and determine its public key length. You can read more about why I wrote this tool. Please let me know if you find a record that doesn’t parse properly and I’ll update my code.

www.mail-tester.com/spf-dkim-check

Check if your domain has these 2 email signatures set up and valid. What's DKIM and SPF? They're 2 effective email signatures against spoofing, phishing or impersonation. When recipients receive your emails, their spam filters automatically poke your d ...

spf.myisp.ch

This online SPF checker visualises and verifies SPF records.