Strategy 12 min read

Email Deliverability in 2025: The Complete Guide to Inbox Placement

By Excelohunt Team · January 15, 2025

Your emails don’t matter if they never reach the inbox. Full stop.

We audit 30+ e-commerce brands every month, and the single most common problem we find isn’t bad copy, weak offers, or ugly templates. It’s deliverability. On average, 15-25% of marketing emails never reach the primary inbox. For brands with poor sending practices, that number climbs to 40-50%.

Let’s do the math. If your list has 100,000 subscribers and you’re losing 25% to spam or promotions, that’s 25,000 people who never see your campaigns. At an average revenue-per-recipient of $0.08, you’re leaving $2,000 on the table per send. Send three campaigns a week, and that’s $312,000 in lost revenue per year. From deliverability alone.

This guide covers everything you need to fix it.

Key Takeaways

Gmail and Yahoo’s 2024 sender requirements are now fully enforced — non-compliance means automatic spam filtering
Authentication (SPF, DKIM, DMARC) is table stakes, not optional
List hygiene is the #1 lever for improving inbox placement rates
Klaviyo’s deliverability tools give you real-time visibility into sender reputation
Engagement-based sending can improve open rates by 20-35% overnight
Warming a new sending domain takes 4-6 weeks when done correctly

What Changed in 2024-2025: The New Rules

Google and Yahoo rolled out strict sender requirements in February 2024, and by 2025 they’re fully enforced with zero grace period. Here’s what matters:

The Non-Negotiables

SPF and DKIM authentication — Every email you send must pass both checks
DMARC policy — You need at least a p=none DMARC record (though p=quarantine or p=reject is better)
One-click unsubscribe — The List-Unsubscribe header must be present and functional
Spam complaint rate below 0.3% — Google’s hard line. Go above this and you’re in trouble
Valid forward and reverse DNS — Your sending IPs must resolve correctly

If you’re using Klaviyo with a dedicated sending domain (which you should be), most of this is handled for you. But “most” isn’t “all.” You still need to verify your setup.

How to Check Your Authentication

In Klaviyo, go to Settings > Domains. You should see green checkmarks next to:

Sending Domain — Your branded sending domain (e.g., mail.yourstore.com)
SPF — Authorized Klaviyo to send on your behalf
DKIM — Cryptographic signature verification
DMARC — Domain-level authentication policy

If any of these show yellow or red, stop everything and fix them first. Nothing else in this guide matters if your authentication is broken.

Understanding Sender Reputation

Think of sender reputation like a credit score. Every email you send either builds or damages it. And just like a credit score, it takes months to build and days to destroy.

The Two Types of Reputation

IP Reputation — The reputation of the server sending your emails. On Klaviyo’s shared infrastructure, this is partially managed for you. On a dedicated IP (available on higher Klaviyo plans), it’s entirely yours.

Domain Reputation — The reputation of your sending domain. This is always yours, regardless of your Klaviyo plan. It’s also what Gmail weights most heavily in 2025.

What Affects Your Reputation

Factor	Impact	Direction
Opens and clicks	High	Positive
Spam complaints	Very High	Negative
Bounces (hard)	High	Negative
Unsubscribes	Medium	Slightly negative
Replies	High	Positive
Time spent reading	Medium	Positive
Delete without reading	Medium	Negative
Moving to Primary tab	High	Positive

The takeaway: mailbox providers are measuring engagement at every level. They know if someone glances at your email for 0.5 seconds and deletes it. That counts against you.

List Hygiene: The #1 Deliverability Lever

We’ve seen brands improve their inbox placement rate by 15-30% in a single week just by cleaning their list. No authentication changes, no content tweaks — just removing the dead weight.

Who to Remove (Or Suppress)

Hard bounces — These should be automatically suppressed by Klaviyo. Verify this is happening.

Soft bounces (3+ consecutive) — If someone’s mailbox has been full or unreachable for three sends in a row, suppress them.

Never-openers (180+ days) — If someone hasn’t opened a single email in 6 months, they’re either not interested or the address is dead. Move them to a sunset flow (more on this below).

Spam complainers — Automatically suppressed by Klaviyo, but check that your suppression list is actually being respected in all flows and campaigns.

Role-based addresses — Emails like info@, sales@, support@ are almost never real subscribers. They dilute your metrics.

The Klaviyo Segment You Need

Create a segment in Klaviyo with these conditions:

Has not opened or clicked any email in the last 180 days
AND has been on the list for at least 90 days
AND has received at least 10 emails

This is your “at risk” segment. For most brands we audit, this segment is 25-40% of their total list. That’s a lot of dead weight dragging down your sender reputation.

Don’t delete them immediately. Run them through a sunset flow first (we wrote a complete guide on that). But stop sending regular campaigns to this segment today.

Ongoing Hygiene Practices

Run list cleaning quarterly — Use a verification service like ZeroBounce or NeverBounce to validate addresses
Monitor bounce rates per campaign — If any campaign exceeds a 2% bounce rate, investigate immediately
Track spam complaint rate in Klaviyo’s Analytics — Stay below 0.1% (Google’s warning threshold is 0.1%, hard limit is 0.3%)
Remove purchased or scraped lists — If you’ve ever added contacts you didn’t collect through opt-in, get rid of them

Engagement-Based Sending

This is the single highest-impact change most brands can make, and it takes 15 minutes to implement.

The Concept

Instead of sending every campaign to your entire list, send only to people who have engaged recently. This immediately improves your open rates, click rates, and sender reputation — which in turn improves deliverability for future sends.

How to Set It Up in Klaviyo

Create three engagement tiers as segments:

Tier 1: Highly Engaged (send everything)

Opened or clicked any email in the last 30 days
OR placed an order in the last 60 days

Tier 2: Moderately Engaged (send 2-3x per week max)

Opened or clicked any email in the last 31-90 days
AND not in Tier 1

Tier 3: Low Engagement (send 1x per week max)

Opened or clicked any email in the last 91-180 days
AND not in Tier 1 or Tier 2

Tier 4: Unengaged (sunset flow only)

Has not opened or clicked in 180+ days

When you launch a campaign, send to Tier 1 first. Two to four hours later, send to Tier 2. This “cascading send” strategy means your initial batch goes to your most engaged recipients, generating strong positive signals that improve inbox placement for the subsequent batches.

The Results

Brands that switch to engagement-based sending typically see:

Open rates increase 20-35% (because you’re not counting unengaged recipients)
Click rates increase 15-25%
Revenue per recipient increase 30-50% (the metric that actually matters)
Spam complaints drop 40-60%

Content and Technical Best Practices

Subject Lines That Don’t Trigger Spam Filters

Spam filters in 2025 are sophisticated — they’re not just looking for “FREE MONEY” in all caps. But certain patterns still trigger them:

Excessive punctuation — “SALE!!! Don’t Miss Out!!!” is a red flag
ALL CAPS words — One is fine for emphasis. Three or more triggers filters
Spammy phrases — “Act now,” “Limited time,” “Buy now” in combination with other signals
Misleading subject lines — Using “Re:” or “Fwd:” when it’s not a reply or forward
Emoji overload — One emoji is fine. Five is a problem

HTML Best Practices

Keep image-to-text ratio balanced — Emails that are 100% images get flagged. Aim for 60% text, 40% images
Always include alt text on images — This helps both accessibility and deliverability
Don’t use URL shorteners in email body — Bitly and similar services are associated with spam. Use full URLs
Limit the number of links — More than 8-10 links in a single email can trigger filters
Include a plain text version — Klaviyo generates this automatically, but verify it’s not empty
Keep email size under 100KB — Large emails get clipped by Gmail, which kills engagement

Infrastructure Checks

Dedicated sending domain — Use a subdomain like mail.yourstore.com or email.yourstore.com, not your root domain
Consistent sending volume — Don’t send 5,000 emails one week and 50,000 the next. Ramp gradually
Warm up new domains and IPs — Start with 500-1,000 emails/day and increase by 25-50% daily over 4-6 weeks
Monitor blacklists — Check MXToolbox weekly to ensure your domain and IPs aren’t listed

Monitoring Deliverability in Klaviyo

Klaviyo gives you several tools to track deliverability. Use them.

Key Metrics to Watch

Delivery Rate — Should be above 98%. Below 95% is a serious problem.

Open Rate (Campaign Average) — With Apple Mail Privacy Protection inflating opens since iOS 15, focus on click rates as your true engagement metric. But a campaign open rate below 15% still signals a deliverability issue.

Click Rate — Your most reliable engagement metric. Healthy benchmark is 1.5-3% for campaigns.

Bounce Rate — Hard bounces above 0.5% per campaign require immediate action. Soft bounces above 2% need investigation.

Unsubscribe Rate — Below 0.3% per campaign is healthy. Above 0.5% means your content or frequency needs work.

Spam Complaint Rate — Below 0.05% is excellent. Above 0.1% is a warning. Above 0.3% and Google will throttle you.

Klaviyo’s Deliverability Hub

Navigate to Analytics > Deliverability in Klaviyo to access:

Domain reputation scores for Gmail, Yahoo, and Outlook
Authentication status with pass/fail indicators
Inbox placement estimates by mailbox provider
Trend data so you can spot problems before they become crises

Check this dashboard weekly. If you see a downward trend in any metric, investigate immediately rather than waiting for it to become a crisis.

Domain Warm-Up Protocol

If you’re setting up a new sending domain or switching ESPs, you need to warm up your domain. Sending 100,000 emails on day one from a brand new domain is the fastest way to land in spam permanently.

Week-by-Week Warm-Up Schedule

Week 1: 500-1,000 emails/day. Send only to your most engaged subscribers (opened in last 30 days).

Week 2: 2,000-5,000 emails/day. Expand to 60-day engaged subscribers.

Week 3: 5,000-15,000 emails/day. Include 90-day engaged subscribers.

Week 4: 15,000-40,000 emails/day. Gradually include your full engaged list.

Weeks 5-6: Full volume. Monitor metrics closely and pull back if any red flags appear.

During Warm-Up, Prioritize

Gmail and Yahoo recipients first — These providers are the strictest but also the most transparent about reputation
Your best content — High engagement during warm-up builds reputation faster
Consistent daily sends — Don’t skip days during warm-up; consistency signals legitimacy
Quick response to bounces — Remove any hard bounces immediately

The Deliverability Audit Checklist

Run through this checklist quarterly:

What to Do When Deliverability Tanks

If you notice a sudden drop in open rates, a spike in bounces, or a blacklist notification, here’s the emergency protocol:

Stop all campaigns immediately — Don’t keep sending into a damaged reputation
Check authentication — Verify SPF, DKIM, DMARC haven’t broken (DNS changes can do this)
Check blacklists — Use MXToolbox to scan your domain and IPs
Review recent campaigns — Did you send to a purchased list? Dramatically increase volume? Send something that generated complaints?
Shrink your audience — For the next 2-3 weeks, send only to your most engaged segment (30-day openers/clickers)
Contact your ESP — If you’re on a shared IP and someone else’s bad behavior is affecting you, Klaviyo support can help
Monitor daily — Track every metric daily until you’ve recovered

Recovery typically takes 2-4 weeks of disciplined, engagement-focused sending.

The Bottom Line

Deliverability isn’t glamorous. Nobody gets excited about DNS records and complaint rates. But it’s the foundation that everything else in email marketing sits on. The best subject line in the world doesn’t matter if it lands in spam.

The brands that take deliverability seriously — authenticating properly, maintaining clean lists, sending to engaged contacts, and monitoring their reputation — consistently see 20-40% higher revenue from email than brands that ignore it.

Fix your deliverability first. Then worry about everything else.

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Tags: deliverabilityemail-marketingauthenticationlist-hygiene

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