Email security
What is an SPF record?
Short answer: An SPF record is a TXT record on your domain, starting with v=spf1, that lists which servers are allowed to send email for you.
The full answer
SPF stands for Sender Policy Framework. Receiving mail servers look it up to check whether the server delivering a message is on your approved list.
The record ends with a rule for everything else: -all (reject), ~all (treat as suspicious) or, dangerously, +all (allow anyone).
v=spf1 include:_spf.google.com -all
Want step-by-step help? Read What Is SPF? How to Set Up an SPF Record.