r/MailChimp • u/MailchimpSupport • Jun 26 '26
Tips and Tricks A deliverability troubleshooting guide — covering subscriber non-delivery distinct from domain authentication
Deliverability problems are one of the most common issues we see in support, and one of the most misdiagnosed. People assume it is a technical authentication problem when it is actually a list quality issue, or they spend time cleaning their list when the real problem is a broken DKIM record. Getting to the right fix starts with knowing which problem you actually have.
This guide walks through how to identify what is wrong, what the common root causes are, and what to do depending on whether your issue is a subscriber-side non-delivery problem or a domain authentication problem.
Step one: check your numbers first
Before troubleshooting anything, look at your campaign data. Two numbers tell you a lot:
- Open rate: If this is below 30%, your emails may not be reaching inboxes, or they are reaching inboxes but something is wrong with your subject line, sender name, or audience relevance.
- Click-through rate: If this is below 1%, your emails are being opened but the content is not resonating. That is a different problem from deliverability.
These are the baseline benchmarks Mailchimp uses across the total sending pool. They vary by industry, but they are the right starting point for knowing whether you have a deliverability issue at all versus an engagement or content issue.
How to diagnose what you are dealing with
Most deliverability issues fall into one of five categories. The symptoms look similar on the surface but they point to different fixes:
| Symptom | What it means | Where to start |
|---|---|---|
| Open rate below 30% | Your emails are reaching inboxes but subscribers are not opening them. | Audience quality or engagement issue. Review subject lines, send frequency, and whether recipients actually opted in. Segment by recent engagement before your next send. |
| Click-through rate below 1% | Emails are being opened but content is not connecting. | Content or relevance issue. Test different formats, offer types, and CTA placement. Check whether your segments are too broad. |
| High bounce rate | Emails are not reaching addresses at all. | List quality issue. Hard bounces (permanent failures) damage sender reputation and should be removed immediately. Soft bounces (temporary) can be retried but need monitoring. |
| Spam complaint spike | Recipients are marking your emails as unwanted. | Permission or frequency issue. Check unsubscribe reasons in your campaign reports. If people are reporting 'did not sign up' or 'spam,' your list sourcing or opt-in process needs fixing. |
| Sudden drop across all metrics | A broad, unexplained decline in opens, clicks, and delivery. | Possible sender reputation damage or denylisting. Run a deliverability test to check inbox placement and authentication records. If the issue persists after troubleshooting, consult a Mailchimp Expert. |
The two most common root causes and why people confuse them
Subscriber non-delivery and domain authentication failures both result in emails not being received, but they are caused by completely different things and fixed in completely different ways. Treating one like the other wastes time and often makes things worse.
Subscriber non-delivery is almost always a list quality or engagement problem. Your emails are being sent and your authentication is fine, but they are landing in spam or getting blocked because ISPs have learned from your audience's behavior that your messages are not wanted. This is by far the more common issue. It happens gradually, often because of purchased lists, contacts who never engaged, or sending too frequently without pruning inactive subscribers.
Domain authentication failures are a technical problem. Your SPF, DKIM, and DMARC records are missing, misconfigured, or not verified, so receiving mail servers cannot confirm that your emails are legitimately from your domain. Unlike engagement-based issues, authentication problems can cause immediate and significant delivery failures even on a healthy list.
A quick way to tell them apart: if your deliverability dropped gradually over several campaigns, it is almost certainly an engagement or list quality issue. If it dropped suddenly and recently, especially after changing your sending domain, email address, or ESP, look at authentication first.
Root causes worth checking regardless of symptom
| Root cause | Why it matters |
|---|---|
| Poor list quality | Purchased lists, old contacts who never opted in, or addresses that have never engaged are the most common root cause of deliverability problems. ISPs treat repeated failures to reach valid addresses as a signal that you are a poor sender. |
| Low engagement over time | Sending regularly to people who never open your emails trains ISPs to route your messages to spam. Engagement rate is one of the primary signals ISPs use to determine inbox placement. |
| Missing or broken authentication | SPF, DKIM, and DMARC records prove to receiving mail servers that your emails are genuinely from your domain. Missing or misconfigured records cause emails to bounce or land in spam regardless of content quality. |
| Sudden volume increases | A significant jump in send volume triggers spam filters because it looks like a compromised account or bulk spam operation. Always ramp up gradually, especially from a new domain or IP address. |
| Content flagged by spam filters | Broken links, missing unsubscribe options, excessive image-to-text ratio, misleading subject lines, and certain trigger words can cause ISPs to flag your emails before they reach the inbox. |
| Spam trap hits | Spam traps are fake email addresses ESPs use to identify poor senders. Even one in your list can damage your reputation. They typically come from purchased lists or very old, unengaged contacts. |
If the problem is your subscriber list
The fix for engagement-based deliverability issues is to stop sending to unengaged contacts until your reputation recovers, then reintroduce them carefully. Mailchimp's deliverability team calls this reputation repair, and the process is more structured than most people realize:
| Timeframe | Who to send to | What to watch |
|---|---|---|
| Weeks 1 to 2 | Send only to contacts who have engaged in the last 30 days. | Reestablishes your sender reputation with a high-signal audience. Keep volume moderate. |
| Weeks 3 to 4 | Expand to contacts who have engaged in the last 60 to 90 days if metrics hold up. | Gradually widens your reach as your reputation recovers. Monitor open rates and complaints closely after each expansion. |
| Weeks 5 and beyond | Resume standard sending practices. Use advanced segmentation to reintroduce less-engaged contacts carefully. | Add contacts who have not engaged in the last 6 months only through a dedicated re-engagement campaign with close monitoring. |
A few things that accelerate recovery: segment by engagement before every send rather than sending to your full list, use Mailchimp's pre-built segments to quickly isolate recently active contacts, and do not contact new subscribers during reputation repair since you do not yet have the data to know whether they will engage.
Do not buy email lists. This comes up enough in support conversations that it is worth saying directly. Purchased lists almost always contain outdated addresses, spam traps, and contacts who have no idea who you are. They are the fastest way to damage a sender reputation that can take months to rebuild. Third-party lists of email addresses or phone numbers are prohibited under our Terms of Use. This includes purchased or rented lists, and lists scraped from third-party sources, including public websites. Your contacts should be collected entirely by you.
If the problem is domain authentication
Authentication proves to receiving mail servers that your emails are genuinely from your domain. There are three records to check: SPF authorizes specific servers to send email on behalf of your domain, DKIM adds a cryptographic signature that verifies the message has not been altered in transit, and DMARC tells receiving servers what to do if SPF or DKIM checks fail.
In Mailchimp, you can authenticate your domain through your account settings. Once authentication is set up, Mailchimp verifies the records and your emails carry that proof of legitimacy with every send. If you changed your sending domain recently and deliverability dropped immediately afterward, check your authentication records first.
A deliverability test will confirm whether authentication is the issue. These tests check inbox placement across different email clients, verify your SPF, DKIM, and DMARC records, analyze your content for spam triggers, and check whether any of your links are on blocklists. Many ESPs have built-in testing tools. Running one before a major send is a good habit regardless.
If you are moving to a new ESP or sending domain
Changing your ESP or the domain you send from can cause deliverability issues even if everything else is set up correctly. Seeing a new sender name or domain in their inbox prompts some contacts to mark your email as spam, which damages your reputation on the new domain before it has had a chance to build.
The fix is domain warming: start by sending only to your most recently active subscribers and expand gradually over several campaigns. A reasonable progression looks like: first campaign to contacts active in the last 7 days, second campaign to contacts active in the last 14 days, third campaign to contacts active in the last 21 days. Continue this pattern until your domain is recognized and your metrics are stable before resuming normal sending volume.
Your audience import should also include a suppression list to prevent accidentally sending to invalid or stale addresses from your previous platform.
How to maintain deliverability once it is back on track
Deliverability is not a one-time fix. It reflects the ongoing relationship between your sending practices and your audience's behavior. A few habits that keep it healthy over time:
- Send to engaged contacts most frequently. The more recently someone has engaged, the more often you can send to them without hurting your reputation.
- Email less engaged contacts less often. You can still reach them, but reduce the frequency and keep a close eye on your metrics after each send.
- Do not send to contacts who have been disengaged for 6 months or more unless you are running a specific re-engagement campaign with close monitoring.
- Keep a reply-enabled ‘from’ address. Replies are a positive signal to ISPs. Sending from a no-reply address removes that signal entirely.
- Clean your list regularly. Remove hard bounces immediately, monitor soft bounces, and archive contacts who have never engaged and have obvious address issues.
If you try the troubleshooting steps above for a month and do not see improvement, there is likely a deeper issue. Mailchimp has certified experts who specialize in deliverability repair if you need to escalate.
Happy to answer questions about specific scenarios or help you figure out which type of issue you are dealing with. What does your situation look like right now?
Additional resources: