Email remains one of the highest-ROI marketing channels, yet inbox placement has become dramatically more sophisticated. Modern filters with ISPs and enterprise mail systems rely on machine learning (ML) to evaluate sender behavior, identity, and audience engagement. The most significant shift in recent years is that filtering is now overwhelmingly engagement-based. Even a well-built campaign can miss the inbox if recipients consistently ignore or delete it.
Marketers who overlook consent, authentication, content quality, and relevance often experience gradual declines in deliverability without understanding why. The following five factors represent the most common and most influential drivers of spam filtering today, updated for 2025.
Table of ContentsInadequate Permission and Poor List HygieneContent That Signals Low Trust or Low ValueLegal and Compliance Shortcuts That Damage TrustMissing or Misconfigured Email AuthenticationSending Messages That Recipients Don’t Care AboutThe Path to Reliable Inbox Placement
Inadequate Permission and Poor List Hygiene
Nothing damages a sender’s reputation more quickly than emailing people who didn’t explicitly agree to receive your messages. Spam complaints, low open rates, high bounce rates, and inactivity accumulate across campaigns, leading mailbox providers to classify your domain as a source of irrelevant or unwanted content. This process doesn’t happen overnight; it often develops from a single purchased list, an old lead database, a poorly framed lead magnet, or a form with ambiguous opt-in language.
Modern list building requires clear expectations and ongoing pruning. Removing long-term unengaged subscribers is not optional. Mailbox providers measure whether recipients interact with your mail, and disengagement is treated as a strong spam-likelihood signal. Brands that practice continuous list hygiene, transparent consent, and proactive audience segmentation maintain inbox access far more reliably.
How to Fix
Use explicit permission: Require clear opt-in for every subscriber and avoid uploading purchased, rented, scraped, or third-party lists that never granted direct consent.
Confirm expectations at signup: Tell subscribers what you will send and how often so engagement patterns align with what mailbox providers expect.
Maintain ongoing list hygiene: Remove hard bounces, spam complainers, role accounts, and chronically inactive subscribers to preserve domain reputation.
Monitor engagement signals: Track opens, clicks, scroll depth, and deletions to determine when a segment is losing interest and needs pruning.
Avoid sending to unengaged contacts: Suppress or sunset subscribers who haven’t interacted in a defined timeframe to prevent negative engagement signals.
Content That Signals Low Trust or Low Value
Keyword triggers and outdated spam words matter far less today than they once did, but content quality still influences deliverability. Filters evaluate layout consistency, HTML integrity, brand clarity, link safety, and expected behavior patterns. Messages with sloppy formatting, mismatched branding, too many images, or no contextual relevance tend to generate low engagement, which is ultimately what harms inbox placement.
The real issue is that low-trust content leads to user actions that teach filters your messages lack value. Deletions without reading, short read times, no scrolling, low click-through, and message-level spam complaints all feed the predictive models that determine inbox placement. Relevant, timely, personalized content has the opposite effect, improving reputation by encouraging positive interaction.
How to Fix
Review content for clarity and value: Ensure every message provides meaningful, timely, or actionable information your audience actually wants.
Optimize HTML structure: Use clean, responsive HTML with proper text-to-image ratios and avoid sloppy or broken formatting.
Ensure all links function correctly: Test every link, CTA, tracking parameter, and landing page to avoid credibility issues and spam-flagging behavior.
Limit link shorteners: Use full URLs or a branded tracking domain to reduce link risk scores and increase transparency.
Keep branding consistent: Align your sender name, from-address, and visual identity so recipients recognize your messages immediately.
Legal and Compliance Shortcuts That Damage Trust
Regulatory compliance has tightened globally, and mailbox providers increasingly detect violations automatically. Missing unsubscribe links, deceptive subject lines, incorrect sender identification, or failure to honor unsubscribe requests within required timelines signal poor sender practices. While compliance laws such as CAN-SPAM, CASL, GDPR, and newer privacy regulations define minimum standards, consumer expectations go far beyond the legal basics.
When compliance feels like an afterthought, trust erodes. Recipients are quicker to mark messages as spam or disengage entirely, and filters take note. Clear consent practices, transparent data usage, and consistently accurate sender information are no longer just legal requirements; they are core components of modern reputation scoring.
How to Fix
Include an easy unsubscribe option: Provide a clearly visible opt-out link and honor requests immediately to meet regulatory and ESP requirements.
Avoid misleading subject lines: Make the subject line truthful and reflective of the email’s actual content to avoid complaints and legal issues.
Maintain clear footer information: Include your physical mailing address and required identifiers for CAN-SPAM, CASL, GDPR, and state-level compliance.
Suppress unsubscribed contacts across all systems: Ensure your CRM, ESP, and marketing automation tools share suppression data to prevent accidental sends.
Audit compliance regularly: Review templates, automations, and signup points to confirm they meet current legal and mailbox-provider expectations.
Missing or Misconfigured Email Authentication
Authentication has become one of the most critical elements of deliverability. SPF and DKIM are foundational, but DMARC is now effectively mandatory for large-volume senders following Gmail and Yahoo’s 2024 requirements. Without proper alignment among these protocols, mailbox providers cannot verify that emails originate from your domain, and filtering becomes significantly more aggressive.
Even with an enterprise-grade ESP, your domain must publish the correct DNS records to ensure authentication passes. Brands that implement DMARC enforcement and alignment often experience noticeable improvements in inbox placement, reduced spoofing, and more consistent domain reputation. Those who skip or misconfigure these records face unpredictable delivery and frequent spam classification.
How to Fix
Authenticate your domain: Configure SPF, DKIM, and DMARC with correct alignment so mailbox providers can verify your sending identity.
Enforce DMARC policies: Move toward quarantine or reject to prevent spoofing and strengthen domain reputation.
Use a dedicated sending domain: Send marketing emails from a branded subdomain to isolate and control sender reputation.
Warm up your domain and IP: Gradually increase volume on new domains or IP addresses to build a positive sending history.
Protect your sending infrastructure: Maintain DNS integrity, enable TLS, and avoid shared IP pools with poor reputations.
Sending Messages That Recipients Don’t Care About
This is the single most crucial factor in 2025. Machine-learning-driven filters evaluate recipient behavior at a granular level: opens, clicks, scroll depth, replies, starred messages, deletions, user-set filters, and how quickly messages are dismissed. These behavioral signals determine whether future messages from your domain belong in the inbox, the promotions tab, or the junk folder.
Irrelevant, repetitive, or overly frequent messaging leads to negative engagement patterns, even if every technical and legal factor is flawless. Brands that understand their audience’s needs, update segments regularly, personalize based on meaningful attributes, and adjust frequency based on engagement signals maintain far stronger deliverability. Relevance is no longer a nice to have but the primary determinant of inbox visibility.
How to Fix
Personalize based on meaningful data: Use behavior, lifecycle stage, purchase history, or stated preferences to increase relevance.
Segment based on lifecycle: Tailor messaging for new leads, current customers, re-engagement segments, and VIPs to drive stronger interactions.
Test message frequency: Adjust cadence to avoid subscriber fatigue or sudden volume spikes that trigger filtering.
Monitor spam complaint rates: Use feedback loops and ISP dashboards to catch relevance problems before they escalate.
Use seed testing and inbox monitoring tools: Validate inbox placement across major providers to confirm your messages remain relevant and properly categorized.
The Path to Reliable Inbox Placement
Email deliverability depends on a balance of permission, trust, authentication, and genuine audience value. Filters reward brands that respect their subscribers and penalize those that treat email as a volume game. A modern program needs clean data, strict compliance, technical accuracy, and consistently relevant content. When recipients interact positively, mailbox providers amplify your visibility. When they disengage, filtering becomes inevitable.
A successful email program today depends on disciplined permission practices, strong authentication, consistent relevance, and a commitment to monitoring engagement signals over time. To ensure those efforts are actually reaching the inbox, you can track and verify inbox placement across major mailbox providers using InboxAware.
©2025 DK New Media, LLC, All rights reserved | DisclosureOriginally Published on Martech Zone: The 5 Reasons Your Email Messages Are Still Ending Up in the Junk Folder in 2025