Email Deliverability — SPF, DKIM, DMARC & Reputation

Deliverability is the ability to get your emails into recipients’ inboxes rather than spam folders. Good deliverability requires proper authentication, quality content, and maintaining a good sender reputation.

Key Factors

1. Authentication

Email authentication proves you’re authorized to send from your domain.

Protocol	Purpose
	Specifies which IPs can send for your domain
	Cryptographically signs emails to verify origin
	Tells receivers how to handle failed authentication

Domain Setup

Configure all authentication records

2. Sender Reputation

Email providers track your sending patterns and recipient engagement: Positive signals:

High open rates
Clicks and replies
Recipients adding you to contacts

Negative signals:

High bounce rates
Spam complaints
Low engagement
Sudden volume spikes

3. Content Quality

Poor content triggers spam filters:

Excessive use of “FREE”, “URGENT”, all caps
Too many images, not enough text
Suspicious links or attachments
No unsubscribe option
Deceptive subject lines

Reputation Best Practices

Maintain Clean Lists

Python
Node.js
Ruby

import ark
from ark import Ark

client = Ark()

def send_to_valid_recipients(recipients, content):
    valid = []

    for recipient in recipients:
        try:
            client.suppressions.retrieve(recipient)
            # Email is suppressed, skip it
        except ark.NotFoundError:
            # Not suppressed, safe to send
            valid.append(recipient)

    if valid:
        return client.emails.send_batch(
            emails=[{**content, "to": [r]} for r in valid]
        )

import Ark from 'ark';

const client = new Ark();

async function sendToValidRecipients(recipients: string[], content: EmailContent) {
  const valid: string[] = [];

  for (const recipient of recipients) {
    try {
      await client.suppressions.retrieve(recipient);
      // Email is suppressed, skip it
    } catch (error) {
      if (error instanceof Ark.NotFoundError) {
        // Not suppressed, safe to send
        valid.push(recipient);
      } else {
        throw error;
      }
    }
  }

  if (valid.length > 0) {
    return client.emails.sendBatch({
      emails: valid.map(to => ({ ...content, to: [to] })),
    });
  }
}

require "ark_email"

client = ArkEmail::Client.new

def send_to_valid_recipients(recipients, content)
  valid = []

  recipients.each do |recipient|
    begin
      client.suppressions.retrieve(recipient)
      # Email is suppressed, skip it
    rescue ArkEmail::Errors::NotFoundError
      # Not suppressed, safe to send
      valid << recipient
    end
  end

  if valid.any?
    client.emails.send_batch(
      emails: valid.map { |r| content.merge(to: [r]) }
    )
  end
end

Never purchase email lists. They contain invalid addresses and uninterested recipients that will damage your reputation.

Warm Up New Domains

When starting with a new domain, gradually increase volume:

Week	Daily Volume	Notes
1	50-100	Send to most engaged users
2	200-500	Expand to recent openers
3	1,000-2,000	Include broader audience
4+	Double weekly	Monitor bounce rates

Monitor Metrics

Track these metrics to catch issues early:

Metric	Healthy Range	Action if Outside
Bounce rate	< 2%	Clean your list
Complaint rate	< 0.1%	Review content, add unsubscribe
Open rate	> 15%	Improve subject lines

Content Guidelines

Subject Lines

Do:

Keep under 50 characters
Be specific and relevant
Personalize when possible

Don’t:

Use ALL CAPS
Add RE: or FW: falsely
Use excessive punctuation!!!
Make false promises

Email Body

Do:

Include both HTML and plain text
Use a readable text-to-image ratio (80% text)
Include your physical address
Add clear unsubscribe link

Don’t:

Use URL shorteners
Include attachments without context
Use hidden text or tiny fonts
Embed forms in email

Technical Setup

Proper Headers

Ark handles most headers automatically, but ensure:

Python
Node.js
Ruby
Go

client.emails.send(
    from_='"Your Company" <hello@yourdomain.com>',  # Friendly name
    to=["user@example.com"],
    reply_to="support@yourdomain.com",  # Valid reply address
    subject="Hello",
    html="<p>Hello!</p>"
)

await client.emails.send({
  from: '"Your Company" <hello@yourdomain.com>',  // Friendly name
  to: ['user@example.com'],
  replyTo: 'support@yourdomain.com',  // Valid reply address
  subject: 'Hello',
  html: '<p>Hello!</p>',
});

client.emails.send_(
  from: '"Your Company" <hello@yourdomain.com>',  # Friendly name
  to: ["user@example.com"],
  reply_to: "support@yourdomain.com",  # Valid reply address
  subject: "Hello",
  html: "<p>Hello!</p>"
)

client.Emails.Send(ctx, ark.EmailSendParams{
    From:    `"Your Company" <hello@yourdomain.com>`, // Friendly name
    To:      []string{"user@example.com"},
    ReplyTo: ark.String("support@yourdomain.com"), // Valid reply address
    Subject: "Hello",
    HTML:    ark.String("<p>Hello!</p>"),
})

List-Unsubscribe Header

For marketing emails, include an unsubscribe header:

Python
Node.js
Ruby
Go

client.emails.send(
    from_="newsletter@yourdomain.com",
    to=["subscriber@example.com"],
    subject="Weekly Newsletter",
    html=content,
    headers={
        "List-Unsubscribe": "<mailto:unsubscribe@yourdomain.com>, <https://yourdomain.com/unsubscribe>",
        "List-Unsubscribe-Post": "List-Unsubscribe=One-Click"
    }
)

await client.emails.send({
  from: 'newsletter@yourdomain.com',
  to: ['subscriber@example.com'],
  subject: 'Weekly Newsletter',
  html: content,
  headers: {
    'List-Unsubscribe': '<mailto:unsubscribe@yourdomain.com>, <https://yourdomain.com/unsubscribe>',
    'List-Unsubscribe-Post': 'List-Unsubscribe=One-Click',
  },
});

client.emails.send_(
  from: "newsletter@yourdomain.com",
  to: ["subscriber@example.com"],
  subject: "Weekly Newsletter",
  html: content,
  headers: {
    "List-Unsubscribe" => "<mailto:unsubscribe@yourdomain.com>, <https://yourdomain.com/unsubscribe>",
    "List-Unsubscribe-Post" => "List-Unsubscribe=One-Click"
  }
)

client.Emails.Send(ctx, ark.EmailSendParams{
    From:    "newsletter@yourdomain.com",
    To:      []string{"subscriber@example.com"},
    Subject: "Weekly Newsletter",
    HTML:    ark.String(content),
    Headers: map[string]string{
        "List-Unsubscribe":      "<mailto:unsubscribe@yourdomain.com>, <https://yourdomain.com/unsubscribe>",
        "List-Unsubscribe-Post": "List-Unsubscribe=One-Click",
    },
})

Handling Issues

High Bounce Rates

A bounce rate above 2% signals list quality issues and will harm your sender reputation. Hard bounces (immediate permanent failures) are automatically suppressed by Ark on first occurrence. If you’re seeing high hard bounce rates:

Identify the source: Are bounces from specific domains or your entire list?
Check for typos: Common typos like gmial.com instead of gmail.com
Verify at signup: Use double opt-in for new subscribers
Clean old lists: Remove addresses that haven’t engaged in 6+ months
Validate before import: Use email validation services before importing bulk lists

Soft bounces (temporary failures) are retried automatically up to 18 times. If many soft bounces convert to hard fails:

Check send volume: You may be hitting rate limits at receiving servers
Review message size: Large attachments can cause rejections
Spread sends over time: Avoid sending to one domain in large bursts

Ark protects your reputation automatically. Hard bounces trigger immediate suppression, preventing repeated delivery attempts to invalid addresses. This keeps your bounce rate low and your sender reputation healthy.

Spam Complaints

Make unsubscribe easy: One click, no login required
Set expectations: Confirm what they’ll receive when signing up
Honor preferences: Send only what users asked for
Remove complainers: Never email someone who complained

Low Open Rates

Check deliverability: Are emails reaching spam?
Improve subject lines: A/B test different approaches
Optimize send time: Test different times of day
Segment your list: Send relevant content to each group

Testing Deliverability

Before launching campaigns:

Send test emails to major providers (Gmail, Outlook, Yahoo)
Check spam folders on each provider
Use seed lists to monitor placement
Review email headers for authentication results

# Check SPF/DKIM/DMARC in email headers
# Look for: Authentication-Results header
# Should show: spf=pass, dkim=pass, dmarc=pass

Monitoring Tools

Postmaster Tools: Google, Microsoft, Yahoo offer insights
Feedback loops: Sign up with major ISPs
Ark webhooks: Monitor bounces and complaints in real-time

Python (FastAPI)
Node.js (Express)
Ruby (Sinatra)

@app.post("/webhooks/ark")
async def handle_webhook(request: Request):
    event = await request.json()

    if event["event"] == "MessageBounced":
        alert_ops(f"Bounce detected: {event['payload']}")

    if event["event"] == "MessageComplained":
        alert_ops(f"Spam complaint from: {event['payload']['message']['to']}")

    return {"status": "ok"}

app.post('/webhooks/ark', (req, res) => {
  const event = req.body;

  if (event.event === 'MessageBounced') {
    alertOps(`Bounce detected: ${JSON.stringify(event.payload)}`);
  }

  if (event.event === 'MessageComplained') {
    alertOps(`Spam complaint from: ${event.payload.message.to}`);
  }

  res.status(200).send('OK');
});

post '/webhooks/ark' do
  event = JSON.parse(request.body.read)

  if event['event'] == 'MessageBounced'
    alert_ops("Bounce detected: #{event['payload']}")
  end

  if event['event'] == 'MessageComplained'
    alert_ops("Spam complaint from: #{event['payload']['message']['to']}")
  end

  'OK'
end

White-Label Deliverability

When running a white-label email platform, deliverability requires additional considerations: Per-Tenant Domains: Each tenant sends from their own verified sending domains with full DKIM, SPF, and DMARC authentication. Per-Tenant Domain Warm-Up: New tenant domains should follow the warm-up schedule above independently. Give each tenant their own domain for proper deliverability. Monitoring Across Tenants: Use per-tenant usage tracking and per-tenant webhooks to monitor deliverability metrics per customer.

Domain Setup

Configure authentication records

Suppression Management

Keep your list clean

Architecture Overview

Multi-tenant architecture

Bounce Handling

Manage bounces and suppressions

Documentation Index

​Key Factors

​1. Authentication

Domain Setup

​2. Sender Reputation

​3. Content Quality

​Reputation Best Practices

​Maintain Clean Lists

​Warm Up New Domains

​Monitor Metrics

​Content Guidelines

​Subject Lines

​Email Body

​Links

​Technical Setup

​Proper Headers

​List-Unsubscribe Header

​Handling Issues

​High Bounce Rates

​Spam Complaints

​Low Open Rates

​Testing Deliverability

​Monitoring Tools

​White-Label Deliverability

Domain Setup

Suppression Management

Architecture Overview

Bounce Handling

Key Factors

1. Authentication

2. Sender Reputation

3. Content Quality

Reputation Best Practices

Maintain Clean Lists

Warm Up New Domains

Monitor Metrics

Content Guidelines

Subject Lines

Email Body

Links

Technical Setup

Proper Headers

List-Unsubscribe Header

Handling Issues

High Bounce Rates

Spam Complaints

Low Open Rates

Testing Deliverability

Monitoring Tools

White-Label Deliverability