None of your email marketing matters if emails don’t reach inboxes.

Deliverability is invisible when it works. When it fails, everything fails. Open rates drop. Campaigns underperform. And the real problem stays hidden because you’re still “sending” emails. They’re just landing in spam.

AI is changing email content and volume. Deliverability best practices are changing too.

What Good Deliverability Looks Like

Let’s set the baseline.

A good email deliverability rate in 2025 falls between 95% and 99%. Anything below 94% indicates problems with sender reputation, authentication, or list hygiene.

The average deliverability rate globally is around 83-85%. That means 15-17% of emails never reach their intended recipients.

Below 80% is poor, indicating significant issues that need urgent attention.

The gap between average and good is substantial. And the gap matters more than you’d think, compounding across every campaign.

The Spam Rate Threshold

Spam complaints are the quickest way to destroy deliverability.

According to Google and Yahoo’s sender requirements, your spam rate must stay below 0.3%. The ideal target is below 0.1%. That’s one complaint per 1,000 emails.

0.1% sounds tiny. For a 10,000-person list, that’s 10 complaints to stay safe. Not much margin.

What triggers complaints:

• Irrelevant content
• Too frequent emails
• Emails recipients don’t remember signing up for
• Difficult unsubscribe process
• Misleading subject lines

AI-generated emails at scale can easily cross these lines if not managed carefully.

Technical Requirements: The Non-Negotiables

Three authentication protocols are now required, not optional.

SPF (Sender Policy Framework)

Tells receiving servers which mail servers can send email on behalf of your domain. Without it, your emails look suspicious.

Setup: Add a TXT record to your domain’s DNS specifying authorized sending servers.

DKIM (DomainKeys Identified Mail)

Adds a digital signature to emails proving they haven’t been modified in transit and actually came from your domain.

Setup: Generate a key pair, add public key to DNS, configure your email platform to sign outgoing messages.

DMARC (Domain-based Message Authentication)

Builds on SPF and DKIM, telling receivers what to do with emails that fail authentication (reject, quarantine, or accept).

Microsoft now enforces strict DMARC requirements for senders of more than 5,000 emails per day. Google and Yahoo have similar mandates.

Setup: Add a DMARC policy to DNS. Start with monitoring mode (p=none), then move to quarantine or reject as you confirm legitimate mail is authenticated.

BIMI (Brand Indicators for Message Identification)

Optional but recommended. Displays your brand logo next to emails in supporting inboxes.

BIMI can boost open rates by up to 21% by making emails instantly recognizable. Also signals trust and legitimacy.

Domain and IP Management

Your sending reputation follows your infrastructure.

Domain Warming

New domains need warm-up before volume sending. Start small and gradually increase.

Typical warm-up schedule:

• Week 1: 20-50 emails/day
• Week 2: 50-100 emails/day
• Week 3: 100-250 emails/day
• Week 4+: Gradually increase to target volume

Send to your most engaged subscribers first during warm-up. High engagement signals build reputation.

IP Warming

Similar principle for new IP addresses. Building positive IP reputation requires gradual volume increases.

Shared IPs (common for smaller senders) pool reputation across users. Your deliverability can suffer from others’ behavior.

Dedicated IPs give you complete control but require more active management and higher volume to maintain reputation.

Subdomain Strategy

Consider using subdomains for different email types:

• marketing.yourdomain.com for marketing emails
• transactional.yourdomain.com for receipts, notifications
• newsletter.yourdomain.com for regular newsletter sends

This isolates reputation. If marketing deliverability drops, transactional emails stay protected.

List Hygiene: Clean Data Wins

Your list quality determines deliverability more than most other factors.

Regular Cleaning

Remove inactive contacts who haven’t opened an email in 6+ months. They’re hurting your metrics without providing value.

Run your list through a validation service before major sends. Identify and remove:

• Invalid email formats
• Typos in domains (gmail.con, yahooo.com)
• Temporary or disposable email addresses
• Known spam traps

Bounce Management

Hard bounces (permanent failures) should trigger immediate removal. Continuing to send to invalid addresses signals poor list management.

Soft bounces (temporary issues) warrant monitoring. Multiple soft bounces become hard bounces.

Spam Trap Avoidance

Sending to purchased lists is the fastest way to hit spam traps. These addresses exist specifically to catch bad senders.

Build lists organically. Double opt-in adds friction but ensures valid, engaged subscribers.

Engagement-Based Sending

Send only to engaged segments. Recent clickers are safer than recent openers, who are safer than inactive subscribers.

Higher engagement rates signal to inbox providers that your mail is wanted.

Content Guidelines for Deliverability

What you write affects whether it gets through.

AI-Specific Considerations

AI-generated content can inadvertently trigger spam filters:

• Generic language patterns that look automated
• Formatting inconsistencies
• Overuse of certain phrases

Review AI output for spam triggers before sending. Look for:

• Excessive punctuation (!!!)
• ALL CAPS words
• Spam-trigger words (FREE, URGENT, LIMITED TIME)
• Too many links
• Poor text-to-image ratios

Subject Line Hygiene

69% of users report email as spam based on subject line alone.

Avoid:

• ALL CAPS
• Excessive exclamation points
• Misleading claims
• Spam-trigger words
• Re: or Fwd: prefixes (unless genuine replies)

Body Content

Stick to clear subject lines and natural, human-sounding copy.

Guidelines:

• Limit links (one or two in cold email, more okay in newsletters to engaged subscribers)
• Balance text and images (text-only or image-only both raise flags)
• Include plain text version alongside HTML
• Avoid URL shorteners (often associated with spam)
• Make unsubscribe easy and visible

Unsubscribe Handling

Gmail rewards clean opt-outs. Hiding your unsubscribe link increases spam complaints.

Best practices:

• Clear unsubscribe link in footer
• Consider above-the-fold unsubscribe for promotional emails
• Process unsubscribes immediately
• Don’t require login to unsubscribe

Every spam complaint you avoid by making unsubscribing easy protects your reputation.

Volume Management

Scale is where many AI-enabled senders get in trouble.

Daily Limits

Cap sends to around 25-40 emails per day per inbox for cold outreach. Marketing emails to opted-in lists can go higher, but watch for warning signs.

Avoiding Spikes

Avoid sudden send volume spikes. If you normally send 5,000 emails weekly and suddenly send 50,000, that’s a red flag.

Gradual increases are fine. Sudden jumps trigger scrutiny.

Multiple Mailboxes

Need higher volume? Use multiple sender addresses or domains. Spread volume across infrastructure.

This also provides fallback if one address develops reputation issues.

Monitoring and Maintenance

Deliverability isn’t set-and-forget.

Key Metrics to Watch

• Bounce rate: Should be under 2% (hard bounces under 0.5%)
• Spam complaint rate: Under 0.1% ideal, never above 0.3%
• Inbox placement rate: Percentage landing in primary inbox vs. spam
• Sender score: Reputation score from various providers

Tools for Monitoring

Mailbox provider tools:

• Google Postmaster Tools (Gmail reputation)
• Microsoft SNDS (Outlook/Hotmail reputation)

Third-party monitoring:

• GlockApps, MailerCheck, etc. for inbox placement testing
• Email validation services for list hygiene
• Deliverability dashboards in major email platforms

Warning Signs

Act quickly if you see:

• Sudden drop in open rates
• Increase in bounces
• Rising spam complaint rate
• Delivery delays
• Placement in spam folder during testing

These often indicate emerging issues before they become crises.

AI-Specific Deliverability Considerations

AI changes the deliverability equation in specific ways.

Volume Scaling

AI makes sending more email easier. That’s not always good.

AI-powered tools enable 300+ personalized emails daily per sales rep. But infrastructure and reputation must scale with volume.

Scale deliberately. Monitor metrics as you increase. Pull back at first sign of issues.

Content Quality

AI-generated content at scale can develop patterns that spam filters recognize:

• Similar structures across many emails
• Overused phrases
• Formatting consistencies that look templated

Vary your AI output. Edit for uniqueness. Don’t send identical-looking emails to thousands of people.

Personalization Balance

AI personalization helps deliverability by increasing engagement. But over-personalization can backfire.

Creepy personalization using data people didn’t know you had drives complaints. Balance relevance with comfort.

Testing AI Output

Before scaling:

• Send AI-generated emails to yourself
• Check spam folder placement
• Run through spam scoring tools
• Test with seed addresses across providers

Catch issues before they hit your full list.

Recovery: When Things Go Wrong

Even careful senders sometimes face deliverability issues.

Diagnosing the Problem

Check:

• Bounce reports for patterns
• Spam complaint sources
• Authentication failures in Postmaster Tools
• Blocklist status (MX Toolbox, etc.)

Immediate Actions

• Pause sending to affected segments
• Review and fix authentication issues
• Remove recently added problematic addresses
• Reduce volume dramatically

Rebuilding Reputation

• Send only to highly engaged subscribers
• Reduce frequency
• Improve content quality
• Gradually increase volume as metrics improve

Recovery takes time. Weeks or months depending on severity.

Blocklist Removal

If you’re on a blocklist:

• Identify which blocklist
• Follow their removal process
• Address the underlying issue first
• Request removal with evidence of resolution

Some blocklists auto-expire. Others require active delisting.

Platform-Specific Considerations

Major inbox providers have specific requirements.

Gmail

Largest consumer provider. Strict on authentication.

• SPF, DKIM, DMARC all required for bulk senders
• Low spam complaint tolerance
• Tabs system affects perceived engagement (Primary vs. Promotions)

Microsoft (Outlook, Hotmail)

Strict DMARC requirements for 5,000+ daily senders.

• Strong spam filtering
• Sender reputation heavily weighted
• Junk folder aggressive

Apple Mail

Privacy features affect tracking.

• Mail Privacy Protection inflates open rates
• Less visibility into actual engagement
• Focus on click-based metrics

Corporate Email (Google Workspace, Microsoft 365)

Often stricter than consumer:

• Admin-controlled spam policies
• Additional filtering layers
• Reputation requirements vary by organization

Building Long-Term Deliverability

Sustainable deliverability comes from consistent good practices.

Fundamentals

• Proper authentication (SPF, DKIM, DMARC)
• Clean, engaged lists
• Relevant, wanted content
• Appropriate volume
• Easy unsubscribe

Ongoing Maintenance

• Regular list cleaning
• Monitoring metrics
• Responding to issues quickly
• Staying current with provider requirements

AI Integration

Use AI to:

• Generate content that passes spam filters
• Optimize send times for engagement
• Personalize appropriately
• Analyze deliverability patterns

But maintain human oversight on:

• Volume decisions
• Content approval
• List management
• Issue response

Getting Started

This week:

• Verify SPF, DKIM, DMARC are configured correctly
• Check current bounce and complaint rates
• Set up Google Postmaster Tools if using Gmail
• Clean obvious invalid addresses from list

This month:

• Implement regular list hygiene process
• Set up deliverability monitoring
• Review AI-generated content for spam triggers
• Establish send volume guidelines

Ongoing:

• Monitor metrics weekly
• Clean list quarterly
• Update authentication as needed
• Adapt to provider changes

For the broader email marketing context, see AI for email marketing: what actually works. For the content side that affects deliverability, check out AI email copywriting techniques.

Deliverability is foundation. Everything else you do in email marketing assumes emails actually reach inboxes. Protect that foundation and everything else becomes possible.