How can I diagnose and fix HubSpot email deliverability issues for a large database with cold emails?
Matthew Whittaker
Co-founder & CTO, Suped
Published 29 May 2025
Updated 18 Aug 2025
7 min read
Dealing with email deliverability issues in HubSpot, especially when you have a large database and are also sending cold emails, can be a complex challenge. It's frustrating when your messages don't reach the inbox, impacting your marketing efforts and business growth. Many factors contribute to these problems, and a holistic approach is often required to diagnose and fix them.
The common assumption that a dedicated IP address alone will solve all issues is often misleading. The root causes typically lie deeper, within your email sending practices, data quality, and how different types of email, like cold outreach, interact with your overall domain reputation. We'll explore how to identify these issues and implement effective solutions.
The challenge of cold emails and list quality
One of the primary reasons for HubSpot deliverability issues with a large database, especially one accumulated over years, is the presence of low-quality or inactive contacts. Daily sign-ups, particularly without double opt-in for marketing communications, can lead to a significant number of bot-generated or temporary email addresses. Even with email verification for product usage, these addresses can still negatively impact your sender reputation when used for marketing.
Sending cold emails from the same domain or a subdomain (even on a separate ESP like HubSpot) used for regular marketing or transactional emails can severely damage your primary domain's health. Mailbox providers see all sending activity linked to a domain. High bounce rates or spam complaints from cold campaigns can lead to your entire domain (and associated IPs) being blocklisted or flagged, affecting all your email streams.
Diagnosing poor deliverability
To start diagnosing the problem, you need to examine specific metrics within your HubSpot account, such as bounce rates (especially hard bounces), spam complaint rates, and open rates. High numbers in any of these areas signal underlying issues. Understanding the specific failure messages you receive for bounced emails can provide crucial clues about server blocks or content-related filtering.
Another critical step is checking if your sending IP or domain (or any associated subdomains) has been placed on any email blacklists (or blocklists). Being listed can severely impede your ability to reach inboxes. You can check your domain reputation using tools like Google Postmaster Tools, which provide insights into your spam rate, IP reputation, and domain reputation. This helps in understanding how mailbox providers view your sending activity. You can also explore an in-depth guide to email blocklists for more information.
Symptoms of poor deliverability
Your emails consistently land in spam folders or Promotions tabs. Low open rates and click-through rates. High bounce rates, especially hard bounces. Increased spam complaints or abuse reports. HubSpot blocking your email campaigns.
Cleaning your database and effective segmentation
Before considering a new domain, your top priority should be cleaning and segmenting your existing database. This involves rigorously removing hard bounces, identified spam traps, and unengaged contacts. While email verifiers are helpful, some problematic addresses, like temporary emails or those with improper formatting, can still get through. You need to stop sending to these immediately. For further insights, you can review HubSpot's email deliverability best practices.
Segmenting your audience based on engagement levels, historical behavior, and email verification results is crucial. This allows you to prioritize sending to your most engaged users while gradually reintroducing less active segments with careful monitoring. This process is essential to improve email deliverability with a large, unengaged contact list.
Highly engaged users: These are contacts with recent opens, clicks, or purchases. They should be your top priority for email campaigns.
Recently inactive users: Contacts who haven't engaged in 3-6 months. Consider targeted re-engagement campaigns.
Cold/inactive users: Those with no engagement in 6+ months. Hold off sending to these until your overall reputation significantly improves.
High-risk contacts: Addresses flagged by verifiers, those that have hard bounced, or known temporary emails. These should be removed or suppressed immediately.
Improving sender reputation and technical setup
Proper email authentication is foundational to good deliverability. Ensure your domain is correctly configured with SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance). Misconfigurations here are common reasons for emails failing to reach the inbox. HubSpot typically guides you through setting these up, but it's crucial to verify their correct implementation regularly. If you are using HubSpot, here is how to improve SPF alignment and email deliverability.
Even if your authentication records are set up, ensuring alignment for SPF and DKIM with your DMARC policy is essential to pass DMARC checks. HubSpot's settings will generally handle this correctly for emails sent through their platform, but custom setups or emails forwarded through other services can cause issues. You can use a simple guide to DMARC, SPF, and DKIM to understand the basics.
If you decide to use a new domain for marketing, proper IP and domain warming is crucial. This involves gradually increasing your email volume over time to build a positive sending reputation with mailbox providers. Starting with your most engaged segments and slowly expanding to larger lists will help establish trust. This is part of how to improve domain reputation using Google Postmaster Tools.
Strategic approaches for cold outreach
Sending cold emails, by nature, carries higher deliverability risks because recipients haven't explicitly opted in. The challenge is balancing growth through outreach with maintaining a healthy sender reputation. It's often recommended to separate cold email campaigns from your primary marketing and transactional email streams by using distinct domains or subdomains and different ESPs. This isolates the risk and protects your main sending reputation. This is critical for B2B cold email deliverability.
Cold email sending best practices
Send from a dedicated domain or subdomain separate from your main marketing domain. Rigorously clean and validate cold email lists to minimize bounces and spam traps. Warm up your cold email sending domain and IP addresses gradually. Personalize cold emails extensively to increase engagement and reduce spam complaints.
Beyond technical separation, the content and personalization of your cold emails are crucial. Generic or irrelevant messages are quickly marked as spam. Focus on highly targeted outreach with valuable content tailored to each recipient or segment. Even with cold outreach, the goal is to drive engagement, which positively influences your sending reputation over time. You can also gain insight from email sender and domain reputation guides.
Conclusion
Resolving HubSpot email deliverability issues for a large database with cold emails isn't a quick fix, but a continuous process that combines rigorous data hygiene, proper technical configuration, and strategic sending practices. Focus on cleaning your lists, segmenting effectively, and ensuring robust authentication.
By addressing the root causes, especially the impact of cold email activity on your overall domain reputation, you can significantly improve your inbox placement and ensure your important marketing messages reach their intended recipients. Continuous monitoring and adaptation are key to maintaining a healthy sending reputation.
Views from the trenches
Best practices
Implement double opt-in for all new marketing sign-ups to ensure genuine interest and prevent bot registrations.
Rigorously segment your existing contact list based on engagement, recent activity, and verification results.
Separate cold email sending to a distinct domain and ESP to protect the reputation of your primary marketing domain.
Regularly monitor your domain and IP reputation using tools like Google Postmaster Tools and address any negative trends immediately.
Common pitfalls
Sending cold emails from the same domain or IP as your marketing emails, leading to cross-contamination of sender reputation.
Neglecting to clean old, unengaged contacts from your database, which can lead to high bounce rates and spam complaints.
Not implementing double opt-in, resulting in a high volume of low-quality or bot-generated email addresses.
Assuming that simply using a new domain will fix underlying list quality issues without proper warming or segmentation.
Expert tips
Consider engaging a deliverability consultant for a comprehensive audit, especially with complex scenarios involving multiple email types and large databases.
Focus on building engagement with your existing active segments before attempting to re-engage older, colder parts of your list.
Invest in robust anti-bot measures at the point of signup to prevent low-quality leads from entering your database.
Prioritize sending relevant, personalized content across all email streams to encourage positive recipient interactions.
Marketer view
Marketer from Email Geeks says that knowing the specific deliverability concerns is the first step to narrowing down the problem.
2024-02-10 - Email Geeks
Expert view
Expert from Email Geeks says that details like business type, address acquisition methods, mail type, specific problem metrics, and rejection messages are crucial for diagnosis, more so than just the ESP.
