Email Deliverability

Deliverability is the measure of how many of your outbound emails actually reach the recipient's inbox (as opposed to their spam folder or being rejected entirely). For AI agents sending automated email, maintaining high deliverability is critical -- a poorly configured sender can get your entire domain blacklisted.

AgentPost provides tools to monitor and optimize your deliverability. This guide covers the key strategies.

Warm-Up Sending Patterns

When you start sending from a new domain or IP address, email providers have no reputation data for you. Sending a large volume immediately triggers spam filters. Instead, gradually increase your sending volume over 2-4 weeks:

Key principles:

• Start with recipients who are most likely to open and engage (this builds positive signals)
• Spread sending throughout the day rather than bursting all at once
• Maintain consistent daily volumes -- large spikes trigger spam filters
• If bounce rates exceed 5%, pause and investigate before continuing

Monitor Bounce and Complaint Rates

AgentPost tracks bounce and complaint metrics and provides a deliverability score (0-100) calculated as:

Score = 100 - (bounce_rate% * 5) - (complaint_rate% * 20)

Healthy Rate Thresholds

AgentPost auto-pauses inboxes when bounce rates exceed the critical threshold to protect your sending reputation. You can re-enable paused inboxes after investigating and resolving the underlying issue.

Subscribe to message.bounced and message.complained webhook events to react to delivery problems in real time.

Content Best Practices

Email content affects deliverability. Spam filters analyze subject lines, body content, HTML structure, and sender behavior patterns.

Subject Lines

• Avoid ALL CAPS, excessive punctuation (!!!), and common spam trigger words
• Keep subject lines concise and relevant to the content
• Avoid misleading subjects (e.g., "Re:" or "Fwd:" on new messages)

HTML Email

• Use a balanced text-to-image ratio (spam filters flag image-heavy emails)
• Include a plain text alternative (text_body) alongside HTML (html_body)
• Avoid using URL shorteners in email links (they are commonly associated with phishing)
• Keep HTML clean -- avoid deeply nested tables or inline styles from word processors

Sending Behavior

• Send from a consistent "from" address for each type of communication
• Use a recognizable sender name that matches your domain
• Do not send to purchased or scraped email lists
• Remove bounced addresses immediately (use message.bounced webhooks)
• Honor unsubscribe requests promptly

Authentication: SPF, DKIM, and DMARC

Proper email authentication is the single most important factor for deliverability. AgentPost configures SPF and DKIM automatically for custom domains and provides DMARC guidance.

See the dedicated SPF, DKIM, and DMARC deep-dive for full configuration details.

Quick checklist:

• SPF record includes AgentPost's SES sending servers
• DKIM signing is enabled with proper DNS records
• DMARC policy is published (start with p=none for monitoring)
• All three records pass verification in AgentPost's domain settings

Dedicated IP Considerations

By default, AgentPost sends through AWS SES's shared IP pool. For high-volume senders, a dedicated IP address provides more control over your sending reputation:

Shared IP (default):

• No warm-up needed (SES maintains the pool's reputation)
• Your reputation is partly shared with other SES users on the same IP
• Good for low-to-medium volume senders

Dedicated IP (via SES):

• Full control over your IP reputation
• Requires careful warm-up (start with very low volumes)
• Best for senders with consistent daily volumes above 10,000 emails
• Configured through AWS SES console, transparent to AgentPost

Inbox Pause Behavior

When AgentPost detects a high bounce rate for an inbox, it automatically pauses outbound sending for that inbox. This prevents further damage to your domain's reputation.

When an inbox is paused:

• Outbound send, reply, and forward requests return a 422 error with the reason
• Inbound email reception is not affected
• Webhook events continue to be delivered
• The pause is logged as a message.rejected event with reason account_paused

To resume sending:

1. Investigate the bounce causes (check delivery events and webhook logs)
2. Clean your recipient lists -- remove addresses that bounced
3. Re-enable the inbox via the API or web console
4. Consider reducing sending volume temporarily

Monitoring with the Deliverability Score

Use the metrics API to track your deliverability score over time:

curl https://api.agent-post.dev/api/v1/metrics/deliverability \
  -H "Authorization: Bearer ap_sk_live_your_key_here"

Response:

{
  "score": 92,
  "bounce_rate": 1.2,
  "complaint_rate": 0.02,
  "delivery_rate": 98.8,
  "period": "7d",
  "total_sent": 4521,
  "total_delivered": 4467,
  "total_bounced": 54,
  "total_complained": 1
}

Review your deliverability score weekly. A declining trend indicates an issue that needs attention before it becomes critical.