What Kind of Email Marketing Causes a Negative Sender Reputation?

Your email marketing strategy can do more than drive engagement and conversions—it also directly affects your sender reputation. And when done poorly, email marketing can damage your reputation with internet service providers (ISPs), leading to low deliverability, spam folder placement, or outright email blocking.

So what kind of email marketing activities actually hurt your sender reputation? In this article, we’ll break down the key mistakes and behaviours that can land your emails in trouble—and what you should avoid to keep your campaigns effective and compliant.

What Is Sender Reputation?

Before diving in, it’s important to understand that sender reputation is a score assigned to your domain or IP address by ISPs like Gmail, Outlook, and Yahoo. It helps them decide whether your email should reach the inbox, be marked as spam, or be rejected altogether.

A poor sender reputation damages your email deliverability and reduces the effectiveness of all your email marketing efforts—even if your list is large and your content is strong.

1. Sending to Purchased or Scraped Email Lists

One of the fastest ways to destroy your sender reputation is to send emails to people who did not give you permission.

Purchased, rented, or scraped lists often contain:

Inactive or non-existent email addresses
Spam traps (set by ISPs to catch bad actors)
People who are likely to mark your email as spam

Sending to these lists typically results in high bounce rates and complaints—both of which severely impact your reputation.

Best Practice: Always build your email list organically, using clear opt-in forms and permission-based practices.

2. High Bounce Rates

A high bounce rate signals that you’re sending to invalid or outdated email addresses. ISPs interpret this as carelessness or spam-like behaviour.

Types of bounces:

Hard bounces – Permanent failures (e.g., non-existent addresses)
Soft bounces – Temporary issues (e.g., full inbox or server issues)

Regularly hitting high bounce rates tells ISPs your list hygiene is poor, and they may begin to block or throttle your emails.

Best Practice: Use a reputable email platform that automatically removes hard bounces from your list (such as Email Blaster UK) and validate your list regularly.

3. High Spam Complaint Rates

When recipients click “Mark as spam,” they send a clear message to ISPs that your emails are unwanted or misleading. A high complaint rate is one of the most damaging metrics for sender reputation.

Causes of spam complaints:

Emails sent without permission
Misleading subject lines
Poor targeting or irrelevant content
No visible unsubscribe link

Best Practice: Set clear expectations at sign-up, provide valuable content, and make it easy for users to unsubscribe rather than report you.

4. Ignoring List Hygiene

Inactive subscribers hurt your engagement metrics and lower your sender reputation over time. ISPs track how many users open, read, click, or delete your emails. If most ignore your messages, that’s a red flag.

Neglecting list hygiene leads to:

Low open and click-through rates
High bounce or spam complaint rates
Being flagged as irrelevant or untrustworthy

Best Practice: Regularly remove or re-engage inactive subscribers. If someone hasn’t opened your emails in 3–6 months, consider suppressing or deleting them.

5. Lack of Email Authentication

If your emails aren’t authenticated using standards like SPF, DKIM, and DMARC, ISPs may not trust that you’re the legitimate sender. This makes it easier for your domain to be spoofed and increases the likelihood your emails will be blocked or filtered.

Best Practice: Ensure your domain is properly authenticated. Most reputable email marketing platforms offer guidance or automate this process.

6. Sending Too Frequently or Inconsistently

Sending emails too often—or on an erratic schedule—can negatively affect your reputation. Too many emails lead to unsubscribes or complaints, while inconsistent sending patterns raise suspicion with ISPs.

Examples of poor sending practices:

Sending daily emails after only a single opt-in
Going months without contact, then suddenly sending a batch
Increasing volume dramatically without warming up

Best Practice: Set a realistic email schedule (e.g., weekly or fortnightly) and stick to it. Gradually ramp up volume if you’re increasing frequency.

7. Misleading or Spammy Content

Even if your list is clean, the content of your emails can trigger spam filters if it contains:

Excessive punctuation or ALL CAPS
Clickbait subject lines
Too many images and little text
Poor spelling or broken links
“Blacklisted” words like “Free!!!”, “Buy now”, “Guaranteed”

ISPs scan email content to assess risk. Spam-like content can lower your trust score and inbox placement.

Best Practice: Write honest, user-focused copy. Avoid sensationalism. Maintain a clean, readable layout with a healthy balance of text and imagery.

8. No Unsubscribe Option or Privacy Notice

Failing to include a visible unsubscribe link and privacy notice can breach regulations like GDPR and PECR—and can seriously harm your deliverability. Users frustrated by the lack of a clear opt-out will often mark your messages as spam.

Best Practice: Always include a one-click unsubscribe link in the footer, along with a link to your privacy policy. It’s legally required and signals transparency to ISPs.

9. Ignoring Engagement Signals

Continuing to send to unengaged subscribers over time tells ISPs your emails aren’t wanted. This leads to:

Lower deliverability
Placement in spam or promotions folders
Damage to your overall sender score

Best Practice: Segment by engagement levels. Send re-engagement campaigns to cold subscribers, and remove them if there’s no response.

Conclusion: Respect and Relevance Drive Reputation

Poor sender reputation is usually the result of neglecting the user experience: sending emails people didn’t ask for, with content they don’t care about, at times they don’t expect.

To avoid a negative sender reputation:

Build a quality list
Send only to people who want to hear from you
Respect inboxes by providing value, relevance, and choice
Monitor metrics and adjust based on engagement

Email marketing works best when you focus on long-term relationships over short-term gains.

A strong sender reputation isn’t built overnight—but it’s worth protecting every time you hit “send.”