What Google publicly emphasizes
Google sender guidelines describe SPF or DKIM for all senders to personal Gmail accounts. For senders above the 5,000 messages per day threshold to Gmail accounts, Google lists SPF, DKIM, DMARC, alignment for direct mail, valid DNS, TLS, spam-rate expectations, message-formatting requirements, and unsubscribe requirements for marketing and subscribed messages.
That makes authentication a readiness baseline, not a complete deliverability audit. Reputation, complaint rates, list consent, message content, volume patterns, and Google Postmaster Tools data can still matter after DNS records look technically correct.