Can someone send email pretending to be you?

SPF is the list of servers allowed to send mail as you. DKIM is a signature that proves a message was not changed on the way. DMARC tells receiving servers what to do when a message fails those checks, and sends you reports.

Two reasons. Without these records, anyone can send invoices or password resets that look like they came from you. And Google and Microsoft now expect them, so mail from a domain without them is more likely to land in spam.

It reads the public DNS records for your domain, the same ones every mail server reads before accepting your mail. Nothing is sent, nothing is changed, and it takes a few seconds.

DKIM keys live under a name your mail provider picks, called a selector. We try the sixteen most common ones. If yours is different, the key is there but we cannot see it. Your provider's DKIM page will say for sure.