Case Study

Improve Email Deliverability with Custom Tracking Domains

How we improved inbox placement by 15-20% for a fast-growing email campaign platform
Author – Sahil Gajjar

Overview

A fast-growing email campaign platform was facing deliverability issues across major inbox providers. While SPF, DKIM, and DMARC were correctly configured, emails still ended up in spam, especially for Gmail and Outlook users.

The root cause was identified: tracking links and open pixels were pointing to third-party domains, which didn’t match the sender’s email domain.

By implementing a Custom Tracking Domain (CTD) system using CNAME records and automated SSL provisioning, we were able to significantly improve email inbox placement and enhance recipient trust.

Challenges Identified

The client faced several technical and usability challenges that were impacting their email deliverability.

Domain Mismatch in Tracking Links

Emails were sent from addresses like john.doe@valensdatalabs.com but contained links from domains like track.example.com, creating trust issues with email filters.

High Spam Placement Rates

Despite valid SPF, DKIM, and DMARC setups, major inbox providers flagged these emails due to third-party redirects and embedded tracking domains.

Manual SSL Management Overhead

Using branded domains for tracking required SSL certificates, but manually issuing and renewing them for every client was not scalable.

Complex DNS Configuration

Non-technical users struggled to configure DNS records correctly, leading to setup failures and delays.

Our Solution

We implemented a comprehensive Custom Tracking Domain (CTD) system with automated SSL provisioning.

Custom Domain UI for Users

  • Built a clean frontend interface allowing users to add and manage multiple CTDs
  • Enabled support for campaign-specific domains, white-labeling, and multi-brand tracking
  • Simplified the process with step-by-step guidance and visual status indicators

CNAME Validation Using Public DNS APIs

  • Validated CNAME setup through DNS-over-HTTPS (DoH) APIs
  • Checked for record conflicts (e.g., existing A/TXT records)
  • Suggested alternative subdomains when the preferred one was already in use
Example Validation Flow:

– User adds: click.valensdatalabs.com
– API checks record type and resolution
– If valid → proceed. If conflict → suggest: clicktrack.valensdatalabs.com

Automated SSL Installation

  • Triggered a Jenkins job post-validation to provision SSL automatically
  • Script handled NGINX config and Certbot certificate setup
  • Enabled HTTPS support without manual intervention
  • Certificates auto-renewed using Certbot’s cron jobs and renewal hooks

NGINX Configuration for Custom Tracking Domains

  • Configured NGINX with individual server blocks to support CNAME-based custom tracking domains for each user.
  • Ensured secure HTTPS delivery of tracking pixels and redirects via the user’s subdomain by installing SSL certificates.

Additional Enhancements

  • Flagged potential wildcard DNS conflicts (*.domain.com) that blocked specific subdomain use
  • Built pre-checks to warn users and suggest valid alternates
  • Added inline helper text for DNS config to guide non-technical users
  • Implemented live domain status and step-wise validation
Additional Enhancements
1. Conflict Detection for Wildcards
  • Flagged potential wildcard DNS conflicts (*.domain.com) that blocked specific subdomain use.
  • Built pre-checks to warn users and suggest valid alternates.
2. UI Improvements to Reduce Errors
  • Inline helper text for DNS config.
  • Live domain status and step-wise validation to guide non-technical users.
3. Scalable Architecture
  • NGINX config templated to support 1,000s of subdomains securely.
  • Efficiently routed all CTD traffic to a single backend, with NGINX dynamically selecting the appropriate SSL certificate per domain using SNI.

Results & Impact

By implementing Custom Tracking Domains with automated DNS validation, SSL provisioning, and branded tracking URLs, we achieved the following improvements:

Email Deliverability Rate Improved by 18%

Achieved higher inbox placement across Gmail, Outlook, and other major providers by eliminating mismatched tracking domains.

Click-Through Rates Increased by 35%

Branded tracking domains built user trust, reducing hesitation to click on links and boosting campaign engagement.

Spam Complaint Rate Reduced by 62%

Aligned sender and tracking domains lowered spam flag triggers, resulting in a significant drop in flagged emails.

DNS Setup Success Rate Increased by 70%

Automated validation and guided domain setup drastically reduced misconfiguration and support queries.

SSL Provisioning Time Reduced by 100%

Migrated from manual SSL handling to full automation with Jenkins and Certbot, eliminating all manual certificate management.

User Onboarding Time Decreased by 80%

Users could complete domain setup in under 15 minutes compared to 2–3 days previously with manual coordination.

Conclusion

By aligning the tracking infrastructure with sender domains using Custom Tracking Domains and automating SSL setup, we solved a major deliverability bottleneck.

This solution not only reduced spam flagging and increased engagement, but also delivered a smoother onboarding experience for clients.

If you’re sending emails on behalf of clients or brands, CTDs are a critical step in maintaining trust, improving engagement, and scaling securely.