SendGrid mail landing in spam: diagnose with auth, engagement, content

Symptom: delivered events on the webhook, but recipients find the mail in spam.

Cause candidates, in order of likelihood:

1. Missing or broken sender authentication. Confirm: check domain auth status in Settings > Sender Authentication. If SPF/DKIM/DMARC are not all validating, receiving servers distrust the mail.
2. Bad engagement. Confirm: high spamreport event counts and low opens relative to volume. Inbox providers demote senders whose mail is ignored or marked as spam.
3. Content and list problems. Confirm: spammy subject lines, no physical mailing address in the footer, no working opt-out, or old purchased lists.

Fix:

1. Complete domain authentication first. It is the highest-leverage single fix.
2. Put your company name in the subject area or header identity, include the physical mailing address and phone in the footer, and give every recipient a clear opt-out. These are the doc's explicit recommendations.
3. Stop mailing unengaged addresses. Continuing to mail people who never open trains the filters against you.
4. Honor spamreport events immediately: suppress the reporter and do not mail them again from any list.

Verification: watch spamreport rates per campaign after the fix, and seed-test to major providers. A falling spamreport rate plus rising opens is the signal.

The deliverability doc: inbox providers weigh engagement (opens vs spam marks), and senders must identify themselves, include a physical address, and offer an opt-out. The domain auth doc: SPF/DKIM/DMARC DNS records assert ownership and message integrity. The event reference: spamreport events fire when a recipient marks the message as spam. Sources: https://docs.sendgrid.com/ui/sending-email/deliverability | https://docs.sendgrid.com/ui/account-and-settings/how-to-set-up-domain-authentication | https://docs.sendgrid.com/for-developers/tracking-events/event