How to Identify the Campaign Causing Spam Issues

When you’re running multiple email campaigns at once, which is a pretty normal thing to do for any business, it can feel impossible to know which one is facing spam issues and dragging your deliverability down.

If you don’t pinpoint it on time, emails that should be hitting the inbox end up in spam, engagement plummets, and your sender reputation takes a hit, thereby landing all your campaigns land in spam.

So, how do you identify the problematic campaign – let’s discuss.

Why it’s hard to identify the culprit campaign

When every campaign uses the same sending domain, the line between “healthy” and “problematic” campaigns gets blurred. Here’s why:

• Shared sender reputation: If one campaign gets flagged by spam filters, your sender reputation gets affected and inbox providers like Gmail and Yahoo may start filtering all of your campaigns.

• Aggregate metrics hide the truth: Many ESPs only show you topline performance across all campaigns, making it hard to spot the outlier.

• Lagging indicators: You don’t get a clear picture of the issue until it’s too late. By the time you realize emails are going to spam, the campaign may already have damaged your domain health.

• No clear benchmarks: There is no context or benchmark for a normal email campaigns’ performance metrics. So, it’s hard to know whether a campaign’s performance is “normal” or a red flag.

This is why most marketers struggle to identify the root cause — they can see deliverability issues, but not which campaign triggered them.

How to identify the campaign causing spam issues

Here is how you can systematically pinpoint the campaign that is triggering spam complaints and affecting your deliverability:

1. Check spam complaint data

Every time a recipient marks an email as spam, mailbox providers like Gmail, Yahoo, or Outlook record it and factor it into your sender reputation. High complaint rates can trigger stricter filtering, reducing inbox placement for all future campaigns.

Start by examining the tools you already have:

• Email platforms (Mailchimp, HubSpot, etc): Most ESPs provide spam complaint reports at the campaign level. Even small spikes such as 0.1–0.2% of recipients can indicate that the message content, frequency, or targeting is off. Pay attention to sudden changes compared to your historical average, as these often precede larger deliverability problems.

• ISP/Postmaster tools (Gmail Postmaster, Microsoft SNDS, Yahoo Complaint Feedback Loop): These tools provide complaint rates by sending domain or IP. By comparing the timing of spikes with your campaign calendar, you can often link a specific email to a rise in complaints. This is especially useful if multiple campaigns were sent around the same time.

2. Compare engagement metrics by campaign

Email service providers (ESPs) track how recipients interact with your emails, including opens, clicks, and unsubscribes. Poor engagement can signal to both recipients and filters that the email is unwanted, increasing the likelihood it will be marked as spam.

When analyzing campaigns, look for:

• Low open rates: If fewer recipients are opening a particular email compared to your usual baseline, it may indicate that the subject line, sender name, or timing isn’t resonating.

• Very low click-through rates: Emails that are opened but ignored suggest the content doesn’t match recipient expectations or needs.

• High unsubscribe rates: A sudden spike in unsubscribes is a clear sign that your message isn’t relevant or is perceived as intrusive.

• Sudden drops compared to normal performance: Compare metrics to historical averages for similar campaigns.

3. Segment your audience and isolate sends

Breaking down your results by audience segments helps identify whether complaints are coming from certain groups and allows you to isolate the problem more effectively.

Consider segmenting your audience by:

• New vs. long-term subscribers: New subscribers may be more sensitive to messaging they didn’t explicitly expect, while long-term subscribers usually engage more consistently.

• Geography or device: Certain regions, languages, or devices can respond differently to your campaigns, especially if local regulations or inbox behaviors vary.

4. Review message content

Modern spam filters are far more sophisticated than they used to be. They don’t just look for obvious “spammy” keywords or punctuation anymore. Instead, they use advanced machine learning models that consider a wide range of signals, including recipient behavior, reputation signals, and subtle patterns in your content.

That said, certain content issues still increase the likelihood of complaints and spam filtering, especially when recipients don’t recognize or engage with your message.

Here’s what to look for:

• Phrases that overpromise or feel like clickbait can increase complaint rates or decrease engagement, both of which harm deliverability over time.

• If recipients don’t immediately recognize who the email is from, they’re more likely to ignore or mark it as spam. Consistent, recognizable branding helps both engagement and filter trust.

• While shortened links aren’t automatically flagged today, links that go through multiple redirects or point to unrelated landing pages can undermine trust and raise spam scores in modern filters.

5. Compare timing and send frequency

Even well-crafted campaigns can trigger complaints if emails are sent too frequently or at inconvenient times. When evaluating timing and frequency, consider:

• Did this campaign go out too soon after a previous one? Sending multiple emails in quick succession can overwhelm recipients.

• Was the email sent outside typical engagement hours for your audience? Emails delivered at inconvenient times often get ignored or marked as spam.

• Did the campaign repeat offers or messaging recently sent? Redundant emails can annoy subscribers and increase complaints.

Many modern ESPs (Email Service Providers) include send-time optimization features that use historical engagement data to determine the ideal time for each recipient. By using these tools, you can automatically schedule emails when each subscriber is most likely to open and interact with them.

6. Use seed testing

Seed testing is a proactive method to catch deliverability issues before they affect your entire audience. By sending your email campaigns to a small internal “seed” list across multiple email clients and devices, you can observe how your emails behave in real inboxes

To implement seed testing, create a small list of internal email addresses that covers all major email providers your audience uses, like Gmail, Outlook, Yahoo, Apple Mail, and mobile clients. Send your campaign to this seed list first and carefully monitor where the emails land: inbox, promotions tab, or spam folder.

Track open and click metrics on these test sends as well. If any issues appear, make the necessary adjustments to content, layout, or links before sending to your full subscriber list.

7. Run a pause-and-test method

Sometimes, even after checking complaints, engagement metrics, content, and seed testing, it can still be unclear which campaign is causing spam issues. In these cases, a controlled pause-and-test method can help isolate the culprit without disrupting your entire email program.

Here’s how to do it effectively:

1. Temporarily stop sending emails from campaigns that might be causing complaints.

2. Restart each campaign individually, sending to a small or full segment.

3. Track spam complaints, unsubscribes, and engagement metrics after each send. If complaints drop significantly when a particular campaign is paused, you’ve likely identified the problematic one.

4. Once the culprit is found, review its content, timing, audience, and frequency. Make necessary adjustments before resuming full sends to protect deliverability.

Conclusion

By combining analytics dashboards and segmentation, you can clearly see which campaign is responsible for your spam issues. Instead of guessing, you’ll know:

• Which campaign triggered deliverability problems

• Whether it’s a campaign-wide issue or batch-specific

• How that campaign compares to your other campaigns

This level of visibility allows you to pause, fix, or adjust the problematic campaign before it damages your entire sender reputation.

So, try out Mailmodo today and ensure for the long run that you’re able to identify the needle in the haystack and fix the issues before they catch up with your other campaigns.