Goal: a sending identity mailbox providers trust.
Step 1. Verify at least one sender identity immediately. Twilio requires authentication or verification before real sending; single sender verification covers one address for tests.
Step 2. Set up domain authentication in Settings > Sender Authentication. Add the SPF, DKIM, and DMARC TXT records to your DNS. Optionally brand the links and use a subdomain for sending.
Step 3. Validate in the console until all records show green. DNS propagation can take a day; do not send production volume from the domain until it validates.
Step 4. On a dedicated IP, set up reverse DNS: add the DNS record SendGrid provides and an A record mapping your domain to the IP. The circular check is A record domain to IP, rDNS IP back to domain.
Step 5. Send test messages to seed addresses at major providers and confirm headers show SPF/DKIM passing and DMARC aligned.
Verify: console shows domain auth validated, rDNS validated, and test headers pass all three checks. Pitfall: changing DNS or the sending domain later silently breaks alignment; re-validate after any change.