The three records that matter
SPF lists the servers allowed to send email for your domain. DKIM signs each message so receivers can verify it. DMARC tells receivers what to do with mail that fails, and sends you reports. Gmail and Yahoo now expect all three from bulk senders.
The SPF 10-lookup limit
Every include:, a, mx and similar term costs a DNS lookup, and SPF allows only 10. Adding one more email service can quietly push you over and break SPF for all your mail.
Frequently asked questions
In your email provider’s settings, or in the headers of an email you sent: look for “s=” in the DKIM-Signature header. Common ones: google, selector1, default, k1.
Start with p=none and a rua= report address, check the reports for a couple of weeks, then move to quarantine and reject.
Many receiving servers reject or spam-folder mail from IPs without a matching PTR record.