How can I diagnose email deliverability issues when using Constant Contact?
Michael Ko
Co-founder & CEO, Suped
Published 23 Jun 2025
Updated 19 Aug 2025
7 min read
When you're using Constant Contact for your email marketing, a sudden drop in email performance can be alarming. The first thought often jumps to being blacklisted (or blocklisted). While being listed on a blocklist can certainly impact your deliverability, it's often not the primary or only cause of emails failing to reach inboxes.
My goal here is to guide you through a systematic approach to diagnose email deliverability issues when you're sending through Constant Contact. We'll look beyond just blocklists and delve into the metrics, configurations, and sending practices that truly dictate whether your emails land in the inbox.
Diagnosing these issues requires a blend of checking your Constant Contact account data, understanding email infrastructure, and sometimes, a bit of detective work. It's about asking the right questions and knowing where to find the answers.
Initial data checks and internal Constant Contact metrics
The very first step in diagnosing deliverability problems with Constant Contact is to access and analyze the data available within your account. This data provides the most direct insights into how your campaigns are performing and where issues might be occurring. Focus on the core metrics Constant Contact provides.
High bounce rates, especially hard bounces, indicate serious list hygiene problems. Constant Contact generally handles automatic suppression of hard bounces, but a sudden spike suggests a deeper issue with how email addresses are being collected. Soft bounces point to temporary problems, like a full inbox or server issues, but if persistent, they can also signal trouble.
Beyond bounce rates, pay close attention to declining open rates and click-through rates. A sharp decrease in these metrics often means that your emails are not reaching the inbox at all, or they are landing in spam folders where recipients don't see them. These engagement metrics are crucial indicators of your sender reputation and content quality.
Common pitfalls with personal test addresses
Timing: You might sign up for a list and expect an immediate email, but campaigns often have specific sending schedules or triggers that aren't instant.
Segmentation: Your test email might not meet the criteria for the segment being targeted by a specific campaign, so you won't receive it even if others do.
Incorrect forms: It's common for websites to have multiple signup forms, and not all may be connected to the active Constant Contact lists you're testing.
List or campaign issues: The problem might stem from how the list is managed, or an error in the campaign setup, rather than deliverability itself. Contact Constant Contact support if you're stuck.
Checking email authentication (SPF, DKIM, DMARC)
Email authentication is the bedrock of deliverability. SPF, DKIM, and DMARC records act as digital signatures, proving to receiving mail servers that your emails are legitimate and haven't been tampered with. Constant Contact typically handles the technical setup of these records for emails sent through their platform, but it's essential to ensure your domain's DNS records are correctly configured to point to their services.
SPF (Sender Policy Framework) specifies which IP addresses are authorized to send email on behalf of your domain. DKIM (DomainKeys Identified Mail) adds a digital signature to your emails, verifying that the content hasn't been altered in transit. DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM, telling receiving servers what to do with emails that fail authentication (e.g., quarantine or reject) and provides valuable reports on your email traffic. Incorrectly configured DMARC can severely impact your deliverability. You can use our free DMARC record generator tool to create one for your domain.
Even though Constant Contact handles much of the complexity, it's still your responsibility to ensure your domain's DNS records are properly set up. You can often find instructions within Constant Contact's knowledge base on how to configure these. If these records are missing or misconfigured, your emails are much more likely to be flagged as spam, even if your content is perfect.
Sender reputation is your domain and IP address's trustworthiness in the eyes of internet service providers (ISPs). Constant Contact manages the IP reputation for the shared IPs their users send from, but your domain's reputation is entirely tied to your sending practices. A poor sender reputation is a major reason why emails go to spam, even if you're not explicitly on a blacklist.
Key factors influencing your sender reputation include your bounce rate, spam complaint rate, engagement levels (opens and clicks), and the quality of your email list. If you're sending to outdated, unengaged, or purchased lists, your reputation will suffer, leading to lower inbox placement. You can learn more about improving your reputation and email reputation with Constant Contact's guide.
While Constant Contact offers tools to help you create engaging emails, the content itself plays a significant role. Emails with too many images, broken links, or spammy keywords can trigger filters, regardless of your reputation. Always use Constant Contact's check for errors tool before sending to catch obvious issues. Even small details, like using an easily recognizable from name, can make a difference.
Symptoms of a deliverability problem
Sudden drop in opens/clicks: Your engagement rates plummet without a clear reason.
High bounce rates: Especially hard bounces, indicating an unhealthy list. Constant Contact helps with this via their bounce management feature.
Test emails not arriving: You send tests to personal addresses and they don't reach the inbox or are delayed.
Increased spam complaints: Recipients are marking your emails as spam more frequently.
Potential root causes
Poor list hygiene: Outdated, invalid, or unengaged subscribers. This can lead to spam traps which hurt your reputation.
Content issues: Spammy language, broken links, image-to-text ratio, or lack of personalization.
Authentication failures: Incorrect or missing SPF, DKIM, or DMARC records for your sending domain. Constant Contact advises on this.
Sender reputation decline: Caused by low engagement, high complaints, or sending to bad addresses.
Blocklisting: Your domain or Constant Contact's shared IP could be on a blocklist. While less common for major ESPs, it's worth checking occasionally.
Beyond the basics: External checks and proactive management
When you're trying to figure out why your Constant Contact emails aren't landing, it's crucial to adopt a holistic diagnostic approach. While the internal metrics in your Constant Contact account are a great starting point, sometimes you need to dig deeper. This often involves looking at your sender reputation from an external perspective and checking for blocklist (or blacklist) issues.
A common misconception is that a blocklist listing is always the primary culprit. In reality, for a large sender like Constant Contact, being directly listed on a major public blocklist that significantly impacts all their users is rare. They have robust systems to monitor and mitigate such issues. However, your specific domain might encounter problems, especially if your sending practices are poor. You can use a blocklist checker to see if your domain is listed on any public blocklists, but remember this is often a symptom, not the root cause.
The key is to proactively manage your email program. This includes regularly cleaning your list to remove unengaged subscribers, maintaining a consistent sending volume, and avoiding content that looks suspicious to spam filters. If you are a consultant trying to diagnose a client's issues, ensuring you have access to their Constant Contact account data and being able to run your own tests to their mailing lists is critical.
For deeper insights, you might also use a dedicated email deliverability testing tool that can provide an inbox placement rate across various ISPs. This helps confirm whether your emails are truly hitting the inbox or being diverted to spam, offering a clearer picture than just anecdotal evidence from a few test addresses.
Maintaining healthy email deliverability
While Constant Contact works hard to maintain its deliverability, the ultimate success of your email program rests on your practices. By consistently monitoring your metrics, adhering to best practices, and promptly investigating any anomalies, you can significantly improve your chances of reaching the inbox. Remember, diagnosing deliverability issues is a continuous process, not a one-time fix.
Stay vigilant with your list hygiene, create engaging content, and understand the technical underpinnings of email sending. Proactive efforts will yield the best long-term results for your email campaigns using Constant Contact.
Views from the trenches
Best practices
Always verify if the Constant Contact account indicates the mail was sent and delivered to specific problematic addresses before assuming a deliverability issue.
Run a seedlist/testlist campaign to your own controlled inboxes and analyze the results. This provides an unbiased view of inbox placement.
Periodically check your domain's authentication records (SPF, DKIM, DMARC) to ensure they are correctly configured and aligned with Constant Contact's requirements.
Regularly clean your email list to remove inactive or bouncing addresses. This improves your sender reputation.
Common pitfalls
Assuming a blacklist (blocklist) listing is the sole cause of deliverability issues; often, it's poor sending practices or content.
Relying solely on signing up for a client's newsletter to test delivery. There could be segmentation, scheduling, or old form issues.
Speculating on deliverability problems without access to Constant Contact's internal sending data or metrics.
Ignoring engagement metrics (opens, clicks) and focusing only on whether emails were 'sent'.
Expert tips
Always compile your own deliverability report using a seedlist test for a client. This helps prove or disprove their theory and identifies focus areas.
Be aware that multiple signup forms on a website can exist, and not all may be connected to active sending lists.
Deliverability issues can sometimes be due to campaign segmentation or list management problems, not just technical mail flow.
Don't discount the impact of seasonal sending patterns; lower mail volumes around holidays might be normal.
Expert view
Expert from Email Geeks says that blocklistings have very little impact on deliverability 99% of the time, and it is more important to focus on whether mail is being delivered successfully.
2023-12-29 - Email Geeks
Expert view
Expert from Email Geeks says to look at bounce rates, open rates, and click rates for high or low spikes. Including personal addresses in your list and seeing if they reach the inbox is a good start.
