How to troubleshoot deliverability issues when ESP and corporate email domains are the same?
Matthew Whittaker
Co-founder & CTO, Suped
Published 20 May 2025
Updated 18 Aug 2025
6 min read
It can be frustrating when emails from your corporate domain start landing in spam folders or not reaching recipients at all. This becomes particularly complex when you use an Email Service Provider (ESP) to send marketing or transactional emails, but your 'From' address shares the exact same domain as your regular corporate communications. This setup, while convenient for branding, often creates a challenging environment for deliverability, as mailbox providers struggle to differentiate legitimate emails from potential impersonations or misconfigurations.
Many organizations face this dilemma, where the marketing team uses an ESP like Mailchimp or Microsoft SendGrid, while the rest of the company relies on Google Workspace or Outlook 365. When both systems send from the same domain, it's crucial to ensure proper configuration to avoid deliverability issues that can impact both types of email traffic. I'll walk you through how to troubleshoot these complexities.
Authentication protocols and domain alignment
When an ESP and your corporate mail server both send emails using the same domain, authentication becomes the cornerstone of your email deliverability strategy. Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM), and Domain-based Message Authentication, Reporting, and Conformance (DMARC) are vital for signaling to mailbox providers that your emails are legitimate.
A common misstep is not including all authorized sending sources in your SPF record. If your ESP's sending IP or domain is not listed, emails sent through them might fail SPF authentication, leading to messages being marked as spam. Similarly, DKIM signatures must be correctly implemented by your ESP to ensure email integrity and authenticity.
Understanding SPF and DKIM for Multiple Senders
Properly configuring SPF, DKIM, and DMARC is essential, especially when using multiple sending services. Each service that sends email on behalf of your domain must be authorized in your DNS records. Incorrect or incomplete records can lead to emails failing authentication checks, which significantly impacts deliverability. If you have any intermittent delivery failures related to SPF or DNS, this is often the first place to look. For a simpler overview, consider a simple guide to DMARC, SPF, and DKIM.
DMARC then builds on SPF and DKIM, requiring at least one of them to align with the 'From' domain. This alignment is critical. If your ESP sends emails that pass SPF or DKIM but don't align with your organizational domain, your DMARC policy could instruct receivers to quarantine or reject those messages, impacting both corporate and ESP-sent emails. Regularly checking your DMARC reports from Google and Yahoo is essential for understanding authentication outcomes and identifying any misalignment issues.
Sender reputation management
Sender reputation is paramount for email deliverability. When your ESP and corporate email domains are the same, their reputations become intrinsically linked. If one experiences issues (e.g., spam complaints, sending to spam traps), it can drag down the reputation of the entire domain, affecting all email streams.
Sending via ESP with shared IP
Shared IP Risk: Your deliverability can be impacted by the sending practices of other ESP clients on the same shared IP address. A few bad senders can get the IP (and by extension, your domain reputation) blocklisted.
IP Warm-up: New IPs or migrating to a new ESP requires careful warming up to build trust with mailbox providers. Otherwise, you may experience deliverability drops.
Sending directly from corporate mail server
Dedicated IP Control: You have full control over your corporate email's IP reputation, which can be beneficial if your internal sending practices are solid.
Domain Overload: High volumes of marketing emails from your main domain, even through an ESP, can negatively affect the reputation of that domain for corporate emails if not managed carefully.
Monitoring your domain's reputation is an ongoing task. Use tools like Google Postmaster Tools to track sender reputation, spam rates, and DMARC failures. Keep an eye on blocklists (or blacklists), as being listed can severely impact your deliverability. Understanding how email blocklists work and what happens when your domain is on one is crucial for timely remediation.
Content, list hygiene, and subdomain strategies
Even with perfect technical setup, your email content and list quality significantly influence deliverability. Spammy content, excessive images, broken links, or misleading subject lines can trigger spam filters, regardless of your authentication. Mailbox providers also analyze user engagement, so low open rates or high complaint rates can hurt your sender reputation.
Maintaining a clean email list is non-negotiable. Sending to invalid or inactive addresses, or worse, to spam traps (also known as honeypots), can quickly ruin your domain's reputation. Regularly clean your lists to remove bounces and unengaged subscribers.
Best practices for content and list hygiene
Content Quality: Focus on valuable, relevant content. Avoid spam trigger words, excessive capitalization, and too many images relative to text. Ensure your image-to-text ratio is balanced.
Engagement Metrics: Monitor open rates, click-through rates, and complaint rates. Low engagement or high complaints signal issues to mailbox providers. High bounce rates can also lead to blocking by Gmail.
List Hygiene: Regularly remove inactive subscribers and hard bounces. Use double opt-in for new subscribers to ensure high-quality lists. Sending to spam traps or honeypots can quickly get your domain blocklisted.
Consider if you can separate your sending practices by using subdomains. For instance, send corporate emails from yourdomain.com and marketing emails from marketing.yourdomain.com. This isolates any potential deliverability issues to the subdomain, protecting your primary corporate domain's reputation. If you're encountering specific issues, such as emails to certain business domains, a subdomain strategy might be particularly helpful.
Troubleshooting and continuous monitoring
To effectively troubleshoot, you need to systematically diagnose the problem. Start by using an email deliverability tester to check your email's spam score and identify any content or technical issues. Compare results from emails sent via your ESP versus your corporate mail server to pinpoint the source of the problem.
Review DMARC aggregate and forensic reports regularly. These reports provide invaluable insights into how various mailbox providers are authenticating your emails. Look for consistent authentication failures, especially those related to SPF or DKIM alignment. Addressing these issues is often the first step in resolving deliverability woes. For general troubleshooting, a proven checklist can be quite beneficial.
Key troubleshooting steps
When facing deliverability challenges with a shared domain, a structured approach to troubleshooting is essential. You need to identify if the issue lies with the ESP-sent emails, corporate emails, or a combination. The Email on Acid blog offers good insights on this. Consider these steps:
Isolate the Problem: Determine if only ESP-sent emails are affected, only corporate emails, or both. This will narrow down your investigation.
Check Authentication Records: Verify your SPF, DKIM, and DMARC records are correctly configured for all sending sources. Use a DMARC record generator tool to ensure proper syntax and values.
Monitor Reputation: Regularly check your domain and sending IP reputation using blocklist checkers and postmaster tools. Being listed on a blocklist (or blacklist) will significantly impact deliverability. Microsoft's Q&A section on email reputation is a good resource.
Finally, maintaining good email deliverability is an ongoing process that requires constant vigilance. By ensuring correct authentication, managing sender reputation, and adhering to content and list hygiene best practices, you can significantly improve the chances of your emails reaching the inbox, even when both your ESP and corporate email domains are the same.
Final thoughts
Successfully navigating email deliverability when using the same domain for both an ESP and corporate email requires a nuanced understanding of technical configurations and sender behavior. It is a balancing act between ensuring all legitimate sending sources are authorized and maintaining a stellar sender reputation. Proactive monitoring and adherence to best practices are critical for consistent inbox placement across all your email streams.
While challenging, this setup offers cohesive branding. With careful attention to SPF, DKIM, and DMARC alignment, consistent monitoring of your domain's health, and meticulous list management, you can overcome common hurdles. Remember, every email counts, and ensuring they reach their intended destination is paramount for effective communication.
Views from the trenches
Best practices
Implement a strict DMARC policy with a 'quarantine' or 'reject' action after careful monitoring, ensuring all legitimate sending sources are covered.
Utilize subdomains for different sending purposes (e.g., marketing, transactional) to isolate reputation risks and manage deliverability more granularly.
Regularly clean your email lists to remove inactive addresses, hard bounces, and known spam traps, improving overall engagement rates.
Monitor your domain's reputation proactively using Postmaster Tools and blocklist checkers, taking immediate action on any alerts or listings.
Common pitfalls
Neglecting to include all ESPs or third-party senders in your SPF record, leading to authentication failures for legitimate emails.
Failing to set up proper DKIM signing for emails sent through your ESP, resulting in messages being flagged as suspicious by mailbox providers.
Not monitoring DMARC reports, which means you miss critical insights into authentication failures and potential domain misuse.
Sending high volumes of marketing emails from your primary corporate domain without proper segmentation or list hygiene, damaging its overall reputation.
Expert tips
Continuously analyze email engagement metrics for both corporate and ESP-sent emails to spot declining trends or unusual spikes in complaints.
Educate internal teams on proper email sending etiquette, especially for mass communications, to maintain a consistent sender reputation.
Consider engaging with mailbox provider postmaster teams directly if you experience persistent issues, providing them with detailed logs and authentication records.
Test email campaigns thoroughly before large sends, utilizing seed lists and deliverability tools to predict inbox placement and identify potential red flags.
Expert view
Expert from Email Geeks says they specialize in taking a big picture look at deliverability to identify what needs to change for emails to consistently land in the inbox.
2021-01-27 - Email Geeks
Expert view
Expert from Email Geeks says a comprehensive audit of all sending practices, including internal and ESP-managed sends, is crucial to prevent conflicting signals to mailbox providers.
Mailchimp or 
Microsoft SendGrid, while the rest of the company relies on 
Google Workspace or 
Outlook 365. When both systems send from the same domain, it's crucial to ensure proper configuration to avoid deliverability issues that can impact both types of email traffic. I'll walk you through how to troubleshoot these complexities.
