Sender Policy Framework (SPF) is an email standard that publishes a list of the servers permitted to send messages for your domain. When a receiving mail server gets a message claiming to be from you, it checks that list. If the sending server is not on it, the message looks suspicious and can be flagged or rejected.
Think of it like a guest list at an event. The bouncer has a sheet of approved names, and anyone showing up claiming to be invited gets checked against it. SPF is that guest list for your domain’s email, and the receiving server is the bouncer doing the check.
The point is to make it harder for attackers to impersonate your address in phishing campaigns. SPF is usually deployed together with two companions, DKIM and DMARC, which add a digital signature and a policy for failures. On its own SPF is helpful; combined with the other two it becomes a strong defence and also improves the deliverability of your genuine email.
There is one practical trap worth knowing. SPF allows only ten DNS lookups per check, and each tool you add with an “include” can eat into that limit. Send through your mail host, a newsletter platform and a CRM, and a sloppy record can quietly blow past ten, at which point every check fails. So keeping the record lean, and removing senders you no longer use, is part of running SPF well rather than a one-time setup you forget about.
At TopDevs we set up SPF along with DKIM and DMARC whenever we wire up a client’s email, so their domain is harder to fake and their real messages actually reach the inbox.
