SPF
A DNS record listing which servers may send for your domain.
Sender Policy Framework is a DNS TXT record that names the IPs and hostnames authorized to send mail for your domain. Mailbox providers check the senders IP against the SPF record. Misconfigured SPF is a common cause of mail going to spam.
reading this as SaaS product teams
A SaaS product sends on behalf of its customers, so the deciding factors are tenant isolation, whether suppressions can be scoped rather than global, and whether support can answer why one specific account did not receive one specific email. Lifecycle automation and transactional sending usually need to coexist.
Applied to spf, that means weighing multi-tenant support, event stream, the suppressions API, and operating track record ahead of the rest, against trial expiry notices, dunning, onboarding sequences, and per-tenant transactional mail.