SPF

SPF (Sender Policy Framework) lists the servers allowed to send email for your domain. It is one TXT record starting v=spf1.

What matters

1. One record only. Two SPF records make receivers fail every message.
2. At most ten DNS lookups. Each include: costs at least one, and nested includes count too. Past ten, SPF fails.
3. The ending. ~all marks other servers as suspicious; -all fails them.

SPF and DMARC

SPF checks the envelope sender, which is often the sending service's own domain. For DMARC, SPF must pass for your domain in the From address. That is called alignment. A service can pass SPF and still fail DMARC.

In SendBop

Authentication settings show your published record and its lookup count. An SPF change can only add services you confirmed under Sending services.