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 teams building autonomous agents
An agent stack treats email as a two-way primitive. Inbound has to arrive as structured JSON a tool call can consume, sends have to be safe to retry when a model loop repeats itself, and every action needs an audit trail. A provider without inbound parsing only solves half the problem.
Applied to spf, that means weighing inbound parsing, idempotency keys, webhook coverage, and operating track record ahead of the rest, against inbound parsing into tool calls and model-generated sends that must not duplicate.