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2026-03-22 · deliverability email dns spf dkim dmarc domain-warming

Email Deliverability for AI Agents: SPF, DKIM, DMARC, and Domain Warming

You've built an agent that sends email. It works in development. Then you deploy to production and discover that half your emails land in spam. The other half bounce.

Deliverability is the unsexy infrastructure problem that determines whether your agent's emails actually reach the inbox. Here's what you need to know.

The Three Authentication Protocols

Modern email authentication rests on three DNS-based protocols. All three need to be configured correctly, or major providers (Gmail, Outlook, Yahoo) will either reject your mail or send it to spam.

SPF (Sender Policy Framework)

SPF tells receiving mail servers which IP addresses are authorized to send email on behalf of your domain. It's a DNS TXT record that lists your allowed senders.

v=spf1 include:_spf.myagentmail.com ~all

This says: "Emails from my domain should come from myagentmail's infrastructure. If they come from anywhere else, treat them as suspicious."

Common mistake: Including too many SPF lookups. The spec limits you to 10 DNS lookups per SPF record. If you're using multiple email services (transactional + agent + marketing), you can hit this limit fast. Consolidate where possible.

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to every outgoing email. The receiving server checks this signature against a public key published in your DNS. If the signature is valid, the server knows the email wasn't tampered with in transit and actually came from an authorized sender.

myagentmail._domainkey.yourdomain.com  CNAME  myagentmail._domainkey.myagentmail.com

DKIM is non-negotiable. Without it, Gmail will almost certainly flag your mail as spam regardless of content.

DMARC (Domain-based Message Authentication, Reporting & Conformance)

DMARC ties SPF and DKIM together and tells receiving servers what to do when authentication fails. It also enables reporting — you get XML reports showing who's sending email from your domain and whether it's passing authentication.

v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com; pct=100

Start with p=none (monitoring only), move to p=quarantine once you're confident in your setup, and eventually move to p=reject for maximum protection.

Recommended progression:

  1. Week 1-2: p=none — collect reports, identify issues
  2. Week 3-4: p=quarantine — suspicious mail goes to spam
  3. Month 2+: p=reject — unauthenticated mail is blocked entirely

Domain Warming

A brand new domain has no sender reputation. Email providers treat unknown senders with suspicion. Domain warming is the process of gradually building that reputation.

The Warming Schedule

Here's a practical warming schedule for an agent domain:

Day Emails per day Target
1-3 5-10 Known contacts who will open and reply
4-7 15-25 Engaged recipients likely to interact
8-14 30-50 Broader audience, still targeted
15-21 50-100 Normal operational volume
22-30 100-200 Scale toward target volume
30+ Target volume Full operation

The key metric during warming isn't send volume — it's engagement. Opens, replies, and "not spam" actions all build positive reputation. Bounces, spam reports, and ignored emails damage it.

Tips for Faster Warming

  1. Start with people who will reply. Internal team members, existing contacts, anyone who will open and engage with the email. Replies are the strongest positive signal.
  2. Keep content short and personal. Long, templated emails look like marketing. Short, conversational emails look like real communication — which is exactly what agents should be sending anyway.
  3. Avoid links in early emails. Links increase spam scoring. During the first week, send plain text with no URLs.
  4. Don't use a brand new domain. If possible, use a domain that's been registered for at least 30 days before you start sending. Age alone doesn't build reputation, but very new domains are flagged.

Why Agent Email Has a Deliverability Advantage

Here's the counterintuitive insight: email sent by well-built AI agents can have better deliverability than traditional marketing email.

Marketing email patterns (bad for deliverability):

Agent email patterns (good for deliverability):

Email providers' spam filters are optimized to catch marketing blasts. An agent sending a personalized, plain-text email to a specific person and receiving a reply looks exactly like legitimate human communication — because functionally, it is.

Common Pitfalls

Pitfall 1: Sending from a Shared Domain

If you're using a shared domain (like the default @myagentmail.com addresses), your deliverability is tied to every other sender on that domain. One bad actor can tank the domain's reputation. For production workloads, always use a custom domain.

Pitfall 2: No Reverse DNS (PTR Record)

If you're running your own mail infrastructure, make sure your sending IP has a valid PTR record that resolves back to your domain. This is handled automatically by email API providers, but worth verifying.

Pitfall 3: Missing Unsubscribe Headers

If your agent sends anything that could be considered commercial (outreach, newsletters, marketing), include List-Unsubscribe headers. Gmail and Yahoo now require them for bulk senders.

curl -X POST https://myagentmail.com/v1/inboxes/{inbox_id}/messages \
  -H "X-API-Key: your-api-key" \
  -H "Content-Type: application/json" \
  -d '{
    "to": "recipient@example.com",
    "subject": "Quick question",
    "text": "Hi — saw your post about scaling ML pipelines...",
    "headers": {
      "List-Unsubscribe": "<mailto:unsubscribe@yourdomain.com>"
    }
  }'

Pitfall 4: Ignoring Bounces

Hard bounces (invalid addresses) damage your reputation fast. Your agent should track bounces and never retry a hard-bounced address. myagentmail surfaces bounce events through the API and WebSocket, so your agent can react immediately.

Monitoring Deliverability

Set up DMARC reporting from day one. Tools like dmarcian or Postmark's DMARC tool parse the XML reports into readable dashboards.

Watch these metrics:

Deliverability isn't a set-and-forget problem. It's an ongoing practice. But the payoff is clear: an agent whose emails consistently reach the inbox is dramatically more effective than one whose messages disappear into spam folders.

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