Deliverability Best Practices

Deliverability is the measure of how successfully your emails reach recipients’ inboxes rather than spam folders or getting rejected entirely. Even well-crafted emails fail if they never arrive. This guide covers the foundational practices that keep your emails landing in the inbox.

Authentication Is Non-Negotiable

Email authentication tells receiving mail servers that you are who you claim to be. Without proper authentication, your emails are far more likely to be filtered or rejected.

Complete Your Domain Setup

Every sending domain in Lettr needs three DNS records configured:

Record	Purpose	What It Does
CNAME	Domain verification	Proves you own the domain and authorizes Lettr to send on your behalf
DKIM (TXT)	Email signing	Adds a cryptographic signature to every email, proving it wasn’t altered in transit
DMARC (TXT)	Policy enforcement	Tells receivers what to do when authentication fails, and where to send reports

Lettr provides the exact DNS record values when you add a domain. Copy them precisely — even small differences cause verification failures. See Sending Domains for the full setup guide.

Set Up a Tracking Domain

Using a custom tracking domain (e.g., track.yourdomain.com) instead of a shared tracking domain improves deliverability. Links in your emails will use your own domain, which builds reputation under your brand rather than sharing it with other senders. See Tracking Domains for setup instructions.

Warm Up New Domains

Mailbox providers treat new sending domains with suspicion. If you send thousands of emails from a domain with no history, spam filters will likely intervene. Warming up means gradually increasing volume so providers can observe consistent, legitimate behavior.

Recommended Warm-Up Schedule

Week	Daily Volume	Notes
1	50–100	Send to your most engaged recipients first
2	200–500	Monitor bounce and complaint rates closely
3	500–2,000	Continue only if metrics remain healthy
4	2,000–5,000	Gradually approach your target volume
5+	Scale as needed	Maintain consistent sending patterns

Sending high volumes immediately from a new domain will damage your reputation before you’ve built one. This damage can take weeks to recover from.

Warm-Up Tips

Start with engaged recipients: Send first to users who regularly open and click your emails. Positive engagement signals help establish reputation.
Be consistent: Send every day during warm-up. Sporadic large sends look suspicious.
Watch your metrics: If bounce rates exceed 5% or spam complaints exceed 0.3%, slow down and investigate before continuing.
Separate transactional and marketing: If you send both types, consider using separate subdomains so marketing reputation issues don’t affect transactional delivery.

Maintain Clean Recipient Lists

Sending to invalid or unengaged addresses is one of the fastest ways to damage deliverability. Mailbox providers monitor your bounce and complaint rates and will throttle or block senders with poor list hygiene.

Process Bounces Immediately

Hard bounces mean the address is permanently undeliverable. Continuing to send to hard-bounced addresses signals to mailbox providers that you don’t maintain your lists. Set up a webhook to handle bounce events in real time:

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

  if (event.type === 'email.bounced') {
    const { to, bounceType } = event.data;

    if (bounceType === 'hard') {
      // Remove from your mailing list immediately
      removeFromList(to);
    }
  }

  res.sendStatus(200);
});

See Bounces for detailed bounce handling guidance.

Use Double Opt-In

Confirm subscriptions before adding addresses to your list. This ensures addresses are valid and that the owner actually wants your emails:

User submits their email address
You send a confirmation email with a unique link
User clicks the link to confirm
Only then add them to your sending list

Remove Unengaged Subscribers

Recipients who never open your emails drag down your engagement metrics. Mailbox providers use engagement signals (opens, clicks) to decide inbox placement. Periodically remove or re-engage subscribers who haven’t interacted in 6–12 months.

Content That Avoids Spam Filters

Even with perfect authentication and a clean list, your email content affects deliverability.

Subject Lines

Do	Don’t
Be clear and relevant	Use ALL CAPS
Keep under 50 characters	Use excessive punctuation!!!
Personalize when possible	Use spam trigger words (FREE, ACT NOW, URGENT)
Set accurate expectations	Mislead about content

Email Body

Do	Don’t
Balance text and images	Send image-only emails
Include a plain text version	Send HTML only
Use your own domain for links	Use URL shorteners (they’re associated with spam)
Add a visible unsubscribe link	Hide or omit the unsubscribe option
Include a physical mailing address	Omit required compliance elements

Every marketing and bulk email should include:

Unsubscribe link — One-click unsubscribe is now required by major providers
Physical mailing address — Required by CAN-SPAM
Reply-to address — Allows recipients to respond

See CAN-SPAM Requirements for detailed legal requirements.

Monitor Your Metrics

Track these key indicators to catch problems early:

Metric	Healthy Target	Warning Sign	Action
Bounce rate	< 2%	> 5%	Clean your list, validate addresses
Spam complaint rate	< 0.1%	> 0.3%	Review content, check unsubscribe visibility
Open rate	> 15%	< 10%	Improve subject lines, check inbox placement
Click rate	> 2%	< 1%	Improve CTAs and content relevance

Open rates are increasingly unreliable due to Apple Mail Privacy Protection and other privacy features that pre-fetch images. Use click rates and direct engagement as more reliable indicators. See Open & Click Tracking Accuracy for details.

Testing Before Sending

Pre-Send Checklist

Send test emails — Send to yourself and colleagues across different email clients (Gmail, Outlook, Apple Mail)
Check rendering — Verify your email looks correct on both desktop and mobile
Verify links — Click every link in the test email to confirm they work
Review content — Read through for spam trigger words and formatting issues
Validate authentication — Check email headers to confirm DKIM is passing

See Test Emails for how to send test emails through Lettr.

Common Deliverability Issues

Emails going to spam

Verify all authentication records (DKIM, DMARC) are passing
Review your email content for spam triggers
Check that you have a visible unsubscribe link
Ensure your domain has built sufficient reputation (warm up if new)
See Emails Landing in Spam for step-by-step diagnosis

High bounce rate

Implement double opt-in for new subscribers
Validate email addresses at the point of collection
Remove subscribers who haven’t engaged in 6+ months
Process bounce webhooks immediately — don’t batch them
See Bounce Diagnosis for interpreting bounce codes

Low open rates

Improve subject lines — test different approaches
Send at times when your audience is most active
Segment your audience for more relevant content
Remove unengaged subscribers to improve overall metrics
Check if Apple MPP is inflating or deflating your numbers

Emails delayed or deferred

Check if you’re sending too fast during domain warm-up
Verify your domain reputation hasn’t been damaged
Look for email.deferred webhook events for specific reasons
Some delays are normal — receiving servers may throttle new senders

Sending Reputation

Build and protect your sender reputation

List Hygiene

Maintain healthy recipient lists

Domain Setup

Configure and verify your sending domains

Bounces

Understand bounce types and handling

Knowledge Base

DNS Guides

Concepts

Email Fundamentals

Best Practices

Compliance & Regulations

Troubleshooting

Use Cases

Glossary

Deliverability Best Practices

Authentication Is Non-Negotiable

Complete Your Domain Setup

Set Up a Tracking Domain

Warm Up New Domains

Recommended Warm-Up Schedule

Warm-Up Tips

Maintain Clean Recipient Lists

Process Bounces Immediately

Use Double Opt-In

Remove Unengaged Subscribers

Content That Avoids Spam Filters

Subject Lines

Email Body

Required Footer Elements

Monitor Your Metrics

Testing Before Sending

Pre-Send Checklist

Common Deliverability Issues

Sending Reputation

List Hygiene

Domain Setup

Bounces

​Authentication Is Non-Negotiable

​Complete Your Domain Setup

​Set Up a Tracking Domain

​Warm Up New Domains

​Recommended Warm-Up Schedule

​Warm-Up Tips

​Maintain Clean Recipient Lists

​Process Bounces Immediately

​Use Double Opt-In

​Remove Unengaged Subscribers

​Content That Avoids Spam Filters

​Subject Lines

​Email Body

​Required Footer Elements

​Monitor Your Metrics

​Testing Before Sending

​Pre-Send Checklist

​Common Deliverability Issues

​Related Topics

Sending Reputation

List Hygiene

Domain Setup

Bounces

Authentication Is Non-Negotiable

Complete Your Domain Setup

Set Up a Tracking Domain

Warm Up New Domains

Recommended Warm-Up Schedule

Warm-Up Tips

Maintain Clean Recipient Lists

Process Bounces Immediately

Use Double Opt-In

Remove Unengaged Subscribers

Content That Avoids Spam Filters

Subject Lines

Email Body

Required Footer Elements

Monitor Your Metrics

Testing Before Sending

Pre-Send Checklist

Common Deliverability Issues

Related Topics