Why Your HubSpot or Klaviyo Emails Still Land in Spam (And What to Fix)

You’ve set up SPF, DKIM, and DMARC. You’ve cleaned your list. You’ve even hired someone to write better subject lines. And yet, your HubSpot or Klaviyo campaigns keep sliding into spam folders – sometimes silently, sometimes catastrophically. The question of why HubSpot emails go to spam haunts marketing teams that have done everything the platform documentation tells them to do. The answer almost always lives in a layer those platforms don’t control. Data Innovation, a Barcelona-based CRM and deliverability consultancy orchestrating over 10 billion emails monthly across more than 10 countries, has documented that over 60% of persistent spam placement issues on platform ESPs trace back to infrastructure-layer failures – shared IP reputation, misconfigured MTA behavior, or subdomain management gaps – rather than content or authentication deficiencies.

Why HubSpot Emails Go to Spam: The Infrastructure Layer Gap

HubSpot and Klaviyo are exceptional platforms. HubSpot excels at CRM, automation, and lifecycle management. Klaviyo delivers sophisticated e-commerce segmentation and real-time behavioral triggers. Neither was built to be a deliverability infrastructure company. And that distinction matters more than most marketing leaders realize.

When you send through a platform ESP, your email passes through several layers before reaching a recipient’s inbox:

1. Application layer – your campaign content, merge tags, templates (HubSpot/Klaviyo handle this)
2. Authentication layer – SPF, DKIM, DMARC records (you configure this, platform guides you)
3. Infrastructure layer – IP pool selection, MTA configuration, subdomain routing, bounce processing, feedback loop integration (this is where the gap lives)

Platform ESPs manage the infrastructure layer at scale for thousands of customers simultaneously. That means shared IP pools, generalized bounce handling rules, and limited control over how your specific sending patterns interact with mailbox provider algorithms. When your emails land in spam despite doing everything “right” inside the platform, the root cause is almost always hiding in layer three.

Three Root Causes Behind Persistent Spam Placement on Platform ESPs

1. Shared Infrastructure and IP Reputation Bleed

Unless you’re on a dedicated IP plan (and most HubSpot and Klaviyo customers aren’t), your emails share IP addresses with other senders. According to Validity’s 2024 Email Deliverability Benchmark Report, shared IP senders experience 2.3x more inbox placement volatility than dedicated IP senders. One bad neighbor running a poorly maintained list can drag your sender score down overnight – and you’ll never see a notification about it.

Even on dedicated IPs, the warm-up and management burden falls on you. HubSpot provides documentation on IP warming, but doesn’t actively manage the ramp schedule, monitor delivery velocity per mailbox provider, or adjust throttling in real time. That operational gap is where placement failures compound.

2. DMARC Alignment Failures at the Subdomain Level

Many organizations set up DMARC at the organizational domain (example.com) but send marketing emails from a subdomain (mail.example.com or news.example.com) without ensuring full alignment. The DKIM signature domain, the Return-Path domain, and the From domain must all align under DMARC policy – and platform ESPs often use their own Return-Path domains by default unless explicitly overridden.

Google and Yahoo’s 2024 sender requirements made DMARC mandatory for bulk senders (5,000+ messages/day). But “having a DMARC record” and “achieving full DMARC alignment across all email streams” are fundamentally different things. Misalignment on a single stream – transactional, marketing, or operational – can erode trust for all streams sharing the same organizational domain.

3. No Dedicated Warming Strategy for New Segments or Campaigns

When marketing teams launch into a new geographic market, reactivate a dormant segment, or migrate from one ESP to another, they need to warm sending infrastructure specifically for that context. Mailbox providers track engagement patterns per sending domain and IP combination. A sudden volume spike to a new segment – even with perfectly clean data – triggers throttling and spam placement at Gmail, Outlook, and Yahoo.

Platform ESPs don’t offer segment-level warm-up orchestration. They can’t, because they don’t control the delivery feedback loops at that granularity. This is a strategic gap, not a product deficiency – it’s simply outside the scope of what an all-in-one marketing platform is designed to solve.

Engagement-Based Filtering Has Changed Everything

If your deliverability strategy still begins and ends with “authenticate and clean your list,” you’re operating on a 2019 playbook. Modern AI-powered spam filters – particularly Gmail’s and Microsoft’s – now analyze behavioral signals continuously and in aggregate:

• Open patterns – not just whether recipients open, but how quickly and how consistently
• Click behavior – depth of engagement, time on page after click-through
• Reply rates – emails that generate replies signal high trust
• Dwell time – how long a recipient keeps an email open before archiving or deleting
• Delete-without-reading rates – a strong negative signal that accumulates per sender

A 2023 study by Mailgun found that senders in the top quartile of recipient engagement had 96% inbox placement, while senders in the bottom quartile – even with perfect authentication – achieved only 68%. Authentication is table stakes. Engagement is the game.

This means deliverability is no longer a set-and-forget infrastructure task. It’s a continuous optimization discipline that requires real-time monitoring of how mailbox providers are responding to your specific sending behavior – something that demands dedicated tooling and expertise beyond what platform ESPs provide in their dashboards.

The 5-Check Diagnostic Framework for Platform ESP Spam Issues

When emails from HubSpot, Klaviyo, or any platform ESP consistently hit spam, run this diagnostic sequence before changing content or blaming the platform:

Check 1: IP Reputation Audit

Pull your sending IPs from email headers and check them against Sender Score (Validity), Talos Intelligence (Cisco), Barracuda Reputation, and Google Postmaster Tools. If you’re on shared IPs, check whether reputation has degraded independently of your own sending behavior. If it has, shared infrastructure is your problem – and no content change will fix it.

Check 2: Full DMARC Alignment Verification

Use a tool like dmarcian, Valimail, or MXToolbox to verify that DMARC alignment passes for all email streams – not just marketing. Check both SPF alignment (Return-Path domain) and DKIM alignment (d= domain) against your From domain. Test from the actual ESP, not just via DNS lookups.

Check 3: Subdomain Isolation Assessment

Verify that your marketing emails, transactional emails, and corporate emails send from separate subdomains. A spam complaint surge on marketing emails should never contaminate your transactional delivery. If everything routes through the same domain or subdomain, you have a blast radius problem.

Check 4: Bounce Handling and List Hygiene Logic

Review how your ESP handles soft bounces versus hard bounces, and what the retry logic looks like. HubSpot, for example, retries soft bounces for up to 72 hours. If a mailbox provider is temporarily rejecting your mail due to reputation (a soft bounce), retrying aggressively can deepen the damage. Compare your ESP’s default bounce rules against best practice thresholds.

Check 5: Engagement Signal Mapping

Segment your list by 30/60/90-day engagement windows and cross-reference spam placement rates per segment. If disengaged segments show dramatically worse placement, you’re triggering engagement-based filtering. The fix isn’t to delete those contacts – it’s to build re-engagement sequences with controlled volume and dedicated monitoring before re-integrating them into main sends.

HubSpot and Klaviyo Are Not the Problem – But They Can’t Be the Full Solution

This is not a critique of platform ESPs. HubSpot remains one of the best CRM and marketing automation platforms available. Klaviyo’s e-commerce integration is genuinely best-in-class. The point is that deliverability infrastructure is a distinct discipline that operates below the application layer these platforms control. Treating your ESP as your deliverability solution is like treating your CMS as your hosting provider – they’re related, but they solve different problems.

When Data Innovation partnered with Nestlé to recover €5M in email-driven revenue, the CRM and automation layer was already well-built. The failures were infrastructural: IP reputation degradation across shared pools, misaligned authentication on regional subdomains, and bounce handling rules that were silently poisoning sender reputation. The platform didn’t cause the problem, and the platform couldn’t solve it.

What to Do When Why HubSpot Emails Go to Spam Becomes a Recurring Question

If your team keeps asking this question – quarter after quarter, campaign after campaign – the answer isn’t another platform migration or another list scrub. The answer is treating deliverability as the infrastructure discipline it has become. Run the five checks above. Map your engagement signals against placement data. Audit your IP and subdomain architecture independently of what your ESP dashboard reports.

And if the gap between what your platform controls and what actually determines inbox placement feels uncomfortably wide, that’s because it is. Closing it requires specialized infrastructure expertise – the kind that complements your HubSpot or Klaviyo investment rather than replacing it. If you want a deliverability audit that starts at the infrastructure layer, reach out to our team to identify exactly where placement is breaking down and how to fix it.