Email Deliverability and Spam Issues

  • Updated on Oct 24, 2025
  • Published on May 2, 2025
  • 3 minute(s) read
  • corey smith
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If your team is experiencing issues with emails being routed to recipients' spam or junk folders or not being delivered at all while using Opensense email signatures or banner campaigns, it's important to understand the technical and content-related factors that influence email deliverability.

Important: Opensense does not control the final delivery of your emails. The reputation and deliverability of your messages are determined by your own email environment and domain reputation, not by Opensense.

Opensense & Deliverability

Opensense is committed to deliverability and security. All signature images and banner assets are white-labeled to your organization's domain, ensuring brand consistency and domain alignment. We employ rigorous testing and adhere to email authentication standards.

Despite these precautions, email deliverability also depends on external factors beyond Opensense's infrastructure. Below are the most common causes for emails being marked as spam.

Key Reasons Emails End Up in Spam

1. Domain Reputation Issues

  • Poor Domain Reputation: Sending to purchased lists, invalid addresses, or engaging in spam-like behavior can harm your domain's reputation. This may lead to blocklisting or spam filtering, which affects the deliverability of even regular one-to-one emails.

  • Recipient Behavior: If recipients frequently mark your messages as spam, delete them without reading, or unsubscribe at unusually high rates, it signals to mailbox providers that your emails are unwanted. These behaviors can negatively impact both your domain and IP reputation, reducing your overall email deliverability.

2. DNS Configuration Issues

  • SPF (Sender Policy Framework): SPF records declare which mail servers are authorized to send email on behalf of your domain. Misconfigured or overly complex SPF records can cause delivery failures or spam filtering.

  • DNS Lookup Limit: SPF records are limited to 10 DNS lookups. Exceeding this limit will cause SPF validation to fail.

    • Solution: Opensense offers an SPF Flattening solution to reduce DNS lookups and ensure RFC compliance with SPF standards. Please reach out to your dedicated Opensense Account Manager for further details.

  • DKIM and DMARC: A failure in DKIM (DomainKeys Identified Mail) or DMARC (Domain-based Message Authentication, Reporting, and Conformance) can flag emails as potentially spoofed or unauthenticated.

3. Content and Formatting Triggers

  • High Image-to-Text Ratio: Emails with more images than text are common spam indicators. It's recommended to maintain a content balance of at least 60% text and no more than 40% images, with an ideal ratio being around 70% text to 30% images for optimal deliverability.

  • Problematic Hyperlinks: Broken, suspicious, or non-secure (non-HTTPS) links, especially those hosted on unrelated domains or using link shorteners (e.g., Bitly, TinyURL), raise red flags for spam filters.

  • HTML Structure: Overuse of tables, excessive whitespace, malformed HTML, or large signature blocks can trigger spam filters.

  • External Media: Static images or banners hosted on unverified domains can hurt sender reputation.

4. Blocklisting and DNS Issues

Your domain or IP may be listed on public DNS blocklists due to past email activity. To help resolve deliverability issues, have your IT team investigate the following:

  • Domain blocklisting: Check if your domain or IP is listed on common DNS-based blocklists (e.g., Spamhaus, Barracuda, SORBS)

  • DNS configuration errors: Ensure records like A, MX, and PTR are properly configured and resolve correctly

  • Mail server responsiveness: Confirm your mail server is reliably accepting connections and not timing out or rejecting traffic

  • SPF, DKIM, and DMARC records: Validate that these authentication protocols are correctly set up and aligned to protect your domain from spoofing

Best Practices to Improve Deliverability

Review Email Headers

Ask your IT team to inspect email headers from messages that were marked as spam. Look for:

  • Authentication-Results

  • Received-SPF

  • DKIM-Signature

  • ARC-Authentication-Results

These can help identify why an email failed authentication or deliverability checks.

Check All Signature and Banner URLs

Ensure that:

  • All links begin with https://

  • They include www. where applicable

  • They do not use link shorteners like Bitly or TinyURL

  • Assets are hosted on your domain or white-labeled subdomain

Missing www. or unsecured links can increase your spam score.

Authenticate Your Email Domain

Verify that your domain has properly configured:

  • SPF: Authorizes which servers can send email on your behalf

  • DKIM: Adds a digital signature to verify email authenticity

  • DMARC: Specifies how to handle emails that fail SPF or DKIM checks

Monitor Your Sending Practices

  • Maintain clean email lists and remove invalid addresses regularly

  • Avoid sudden spikes in email volume

  • Ensure recipients have opted in to receive your communications

  • Make it easy for recipients to unsubscribe if needed

When to Contact Opensense

If you've validated all the above and are still experiencing deliverability issues:

  • Contact us immediately with example email headers or timestamps

  • We'll investigate and resolve any issues within our control or infrastructure

Final Note

Opensense supports over 500 SMB and enterprise clients, including Fortune 500 companies and multinational organizations. Deliverability is our top priority, and you can be confident your signatures and banners are deployed securely and professionally.

Need Help?

For further assistance, contact Opensense Support: