Why Is My Email IP or Domain Blacklisted? Full Guide

Sometimes the  IP addresses and domains you use in email campaigns get blacklisted without you knowing “why”.

When that happens, your emails can get blocked or pushed straight to spam folders before prospects ever see them. 

And the impact can be brutal. 

At SmartReach.io, we’ve seen so many start-ups lose significant pipelines within days simply because their emails weren’t getting through. 

In this blog, we’ll break down why blacklisting happens, how it affects email delivery, and what you can do to detect, resolve, and prevent it.

What is email blacklisting and how does it work?

Email blacklists are security databases used to protect people from spam, malware, and other unwanted messages. 

Source

When your IP address or domain ends up on one of these lists, email providers like Gmail, Outlook, and Yahoo rely on that information to decide whether your emails get delivered, blocked, or sent to the spam folder.

There are two main types:

• IP blacklists flag the specific server your emails are sent from.
  
• Domain blacklists target your entire domain (like yourcompany.com), which can follow you even if you switch email services or IPs.

How do blacklists track and flag problematic email senders?

Blacklist providers use monitoring systems to track email behavior across the internet. 

They analyze factors like:

• Recipient complaints: When people mark emails as spam, these complaints get tracked and associated with the sending IP or domain.

• Bounce patterns: High bounce rates signal poor email list quality, which blacklist providers interpret as potential spam behavior.

• Volume spikes: Sudden increases in email volume from new IPs often trigger automated monitoring systems.

• Content analysis: Some blacklists scan email content for spam-like characteristics or malicious links.

• Behavioral patterns: Sending to many invalid addresses or hitting spam traps raises immediate red flags.

Is IP blacklisting different from domain blacklisting in emails?

Yes,  IP and domain blacklists are different.

Here’s how they differ

Aspect	IP Blacklisting	Domain Blacklisting
What it targets	The sending server’s IP address	Your actual email domain (e.g. yourcompany.com)
Impact scope	Affects all emails sent from that IP address	Affects all emails sent from your domain, no matter the IP or service used
Common in	Shared or dedicated IP services	Any business using a custom domain
Cause example	Another user’s spammy activity on shared IP, or your own server getting compromised	Poor sending practices, domain reputation issues, or domain spoofing
Persistence	Another user’s spammy activity on a shared IP, or your own server getting compromised	Follows your domain — switching services/IP won’t help until the domain reputation is fixed
Difficulty to resolve	This can be resolved by switching to a new IP (if available)	Harder — requires cleaning up domain reputation and working with blacklist providers
Detection by providers	Some blacklists track only IPs	Generally, it is easier to switch IP or request removal
Effect on deliverability	May block or spam-folder emails for providers that check IP blacklists	Broader impact across providers — domain blacklisting can kill inbox placement everywhere
Examples of blacklists	Spamhaus SBL (IP-focused), Barracuda	SURBL (domain-focused), URIBL, Spamhaus DBL
Reputation recovery	Often quicker, especially if using a reputable ESP that rotates IPs	Can take longer; requires sustained good sending practices and sometimes direct negotiation

Why is your email  IP or domain “blacklisted”?

Let’s break down the most common reasons senders end up blacklisted, so you know what to watch for (and how to avoid them).

Reason #1: Previous spam reports and complaint history

This is something many sales professionals don’t realize: spam complaints accumulate over time and create a permanent record associated with your sending reputation. 

Even if you’ve cleaned up your practices, past complaints can continue to haunt your email deliverability.

When recipients mark your emails as spam, this information gets shared with blacklist providers through feedback loops. 

Major email providers like Gmail and Yahoo automatically report these complaints to reputation tracking services. 

Here’s what triggers the most complaints:

• Cold outreach without research: Sending generic sales emails to people who have no connection to your business or industry creates immediate spam complaints.

• Purchased email lists: People on bought email lists never gave you permission to email them, leading to high complaint rates within days of your first campaign.

• Ignoring unsubscribe requests: Continuing to email people after they’ve asked to be removed generates complaints and potential regulatory violations.

• Misleading subject lines: When your subject line doesn’t match your email content, recipients feel deceived and hit the spam button.

• Poor timing and frequency: Emailing too often or at inappropriate times increases the likelihood of complaints.

The tricky part is that complaint thresholds are often very low. 

Some blacklist providers will flag senders with complaint rates as low as 0.1%, meaning just one complaint for every 1,000 emails sent can trigger blacklisting.

Reason #2: Association with malicious activity

If your email infrastructure gets compromised or associated with malicious activity, you can end up on blacklists within hours, and getting removed becomes much more difficult.

• Compromised email accounts: When hackers gain access to your email accounts, they often use them to send spam or phishing emails. Even a few malicious emails sent from your domain can trigger immediate blacklisting.

• Server security breaches: If your email server gets hacked, it might be used to relay spam without your knowledge. Blacklist providers detect this activity quickly and add the compromised IP to their lists.

• Malware infections: Computers infected with malware sometimes send spam emails automatically. If this happens from your business network, your domain could get associated with malicious activity.

• Phishing associations: If your domain gets spoofed in phishing attempts (even without your involvement), some blacklist providers might flag it as a precautionary measure.

• Link reputation issues: Including links to websites that have been flagged for malware or suspicious activity can get your emails blocked, even if your own content is legitimate.

What surprises most sales managers is that blacklisting often correlates with their highest-performing campaign periods. The increased volume and urgency that drive great quarters can also trigger automated systems that protect email users from spam.

Reason #3: Inherited reputation problems

Sometimes you get blacklisted through no fault of your own, simply because you’re using an IP address or domain that had problems in the past.

• Previous IP owner issues: When you start using a new email service or dedicated IP, you might inherit reputation problems from whoever used that IP before you. This is especially common with cloud-based email services that recycle IP addresses.

• Domain history: If you purchase a domain that was previously used for spam or malicious activity, you inherit its negative reputation. This can happen even if the domain was parked or inactive for years.

• Shared hosting problems: When using shared email services, other customers’ bad behavior can affect everyone on the same IP. One spammer on your shared server can get the entire IP blacklisted.

• Subdomain associations: Sometimes blacklist providers flag entire domain families. If someone creates a malicious subdomain under your main domain (through a security breach), it could affect your entire domain’s reputation.

This type of blacklisting is particularly frustrating because you’re paying the price for someone else’s mistakes. 

However, most blacklist providers will work with you to resolve inherited reputation issues once you demonstrate that you’re a legitimate sender.

Reason #4: Poor sending practices that accumulate over time

Many senders don’t realize that seemingly minor poor practices can accumulate into major reputation problems that eventually trigger blacklisting.

• List hygiene neglect: Continuing to email addresses that consistently bounce builds a negative reputation over time. Blacklist providers track bounce patterns and flag senders who don’t properly manage their lists.

• Permission issues: Sending to people who didn’t explicitly opt in to receive your emails, even if you have their contact information from other sources, can slowly build complaint rates.

• Content quality problems: Consistently sending emails with poor formatting, broken links, or content that recipients don’t find valuable leads to gradual increases in spam complaints.

• Engagement pattern issues: If your emails consistently get low open rates and high delete rates without reading, algorithmic systems interpret this as unwanted mail.

• Volume management mistakes: Rapidly increasing your email volume without proper warming procedures can trigger automated blacklisting systems.

• Authentication inconsistencies: Failing to properly set up and maintain email authentication (SPF, DKIM, DMARC) creates trust issues that compound over time.

Reason #5: Technical misconfigurations that raise red flags

Technical problems with your email setup can make you look like a spammer to automated monitoring systems, even when your content and practices are perfectly legitimate.

• Missing or incorrect email authentication: Not having SPF, DKIM, and DMARC records properly configured makes your emails appear suspicious to receiving servers.

• IP warming failures: Sending high volumes immediately from a new IP address without gradually building a reputation triggers spam detection systems.

• Inconsistent sending patterns: Dramatic changes in sending volume, timing, or content patterns can trigger algorithmic suspicion.

• Port and protocol issues: Using non-standard ports or protocols for email sending can raise security flags with some monitoring systems.

These technical issues are often overlooked because they seem minor, but they can be the tipping point that moves you from “questionable” to “blacklisted” in automated systems.

Recommended read: How to set up SPF, DKIM & DMARC to keep emails out of spam?

Impact of blacklisting on email deliverability

When your domain or IP ends up on a blacklist, it directly affects whether your emails ever make it to your recipients. 

The damage can be immediate and sometimes hard to detect at first until your metrics start to tank. 

Blacklisting doesn’t just disrupt email deliverability at the moment; it can harm your email sender reputation for weeks or months, and cost your business real revenue.

Here’s how blacklisting typically impacts your email program:

👉 Complete blocking by providers

Major email services (like Gmail, Outlook, and Yahoo) can reject your emails entirely based on blacklist data. 

You’ll often get bounce errors such as:

• 550 5.7.1 Email rejected due to security policies
  
• 554 5.7.1 Rejected due to DKIM failure
  
• 550 SC-001 Mail rejected for policy reasons

Different providers rely on different blacklists, so you might see mixed results across inboxes.

👉 Automatic spam folder placement

Your emails are delivered but silently land in spam, so prospects never see them. Open and click rates drop sharply, and engagement flatlines.

Sender Score can fall from excellent to poor in just days and rebuilding trust takes time.

👉 Pipeline and revenue loss

Blacklisting during a key campaign means fewer leads, missed opportunities, and direct revenue impact often when it hurts most.

👉 Brand trust damage

If your domain is associated with spam or security warnings, it weakens your credibility with prospects and customers.

👉 Long-term inbox placement challenges

Even after removal from blacklists, email providers may keep your domain flagged for caution making full recovery slower.

How to detect if you’re blacklisted?

Blacklisting often flies under the radar until your email performance suddenly drops. The good news? With the right checks, you can catch and fix it early. 

Here’s how to spot the signs and confirm if your domain or IP is blacklisted:

Recognizing the warning signs in your metrics

The first signs of blacklisting often show up in your email campaign metrics before you realize there’s a technical problem. 

Knowing what to look for can help you catch blacklisting issues quickly.

• Sudden delivery rate drops: If your emails were consistently reaching 95%+ of recipients and suddenly drop to 70% or lower, blacklisting is a likely culprit.
• Increased bounce rates: Hard bounces increasing beyond 2-3% often indicate delivery problems related to reputation issues.
• Open rate crashes: Open rates falling below 5% when they previously averaged 15-25% suggest emails aren’t reaching inboxes.
• Zero reply rates: Complete absence of replies to messages that previously generated responses indicates serious deliverability problems.

Professional email platforms like SmartReach.io include built-in blacklist monitoring that alerts you immediately when reputation issues arise, eliminating the need for manual checking.

Using blacklist checker tools and monitoring services

• MX Toolbox blacklist check: Go to mxtoolbox.com/blacklists.aspx and enter your domain or IP address. 
• The tool checks your status against over 100 different blacklists simultaneously and shows you exactly which lists have flagged you.
• MultiRBL.valli.org: Another comprehensive free checker that queries multiple blacklists and provides detailed results about why you might be listed.
• Email monitoring services: Tools like GlockApps, InboxAlly, and Email on Acid offers ongoing reputation monitoring that alerts you when deliverability issues arise.

Check your status weekly, not just when you suspect problems. Early detection makes resolution much easier and less disruptive to your outreach efforts.

Bounce messages and delivery reports

Bounce messages contain valuable diagnostic information that can help you identify blacklisting issues before they become severe.

Hard bounce analysis: Look for specific error codes like “550 5.7.1” which often indicate reputation or authentication problems that could lead to blacklisting.

SMTP error codes: Codes beginning with 5xx are permanent failures often related to reputation, while 4xx codes are temporary but can indicate developing problems.

Keep records of bounce messages and error patterns. This documentation becomes valuable when working with blacklist providers to resolve listing issues.

How Can I Remove My IP or Domain from Blacklists to Improve Deliverability?

Getting off a blacklist starts with addressing the root cause. 

First, identify exactly which blacklists have flagged your IP or domain using tools like MX Toolbox different lists have different removal processes. 

Before you request removal, fix the issue that triggered the blacklisting. 

This could mean cleaning your email list, securing compromised accounts, or setting up proper email authentication (SPF, DKIM, DMARC). 

Once resolved, follow each blacklist’s removal process some offer automated tools, while others require manual review and proof that the issue is fixed. 

Keep in mind, removal can take anywhere from a few hours to several weeks, depending on the severity of the problem and the specific blacklist.

For detailed step-by-step instructions on removing your IP or domain from specific blacklists, including proven strategies for working with major blacklist providers and handling complex removal cases, read our comprehensive guide on how to remove your IP or domain from blacklists to improve email deliverability.

Global blacklist monitoring with SmartReach.io

When your IP or domain gets blacklisted, your emails can get blocked or sent straight to spam, and most of the time, you won’t even know it until your open rates drop or your prospects stop replying. 

That’s why protecting email deliverability is essential if you want your outreach to succeed.

SmartReach.io offers a complete set of deliverability tools designed to help your emails reach inboxes. 

From email verification (to remove invalid addresses), email warmup (to build a positive reputation), to inbox rotation and ESP matching (to avoid spam filters), SmartReach is built to safeguard your sender reputation at every step.

A major part of this is Global Blacklist Monitoring. 

Here’s how it helps:

• Continuous monitoring: SmartReach automatically checks if your domain or IP appears on any of the top global blacklists.

• Instant alerts: The moment there’s an issue, you’ll be notified so you can take quick action before your outreach is affected.

• Auto-pause protection: Sending from the blacklisted account is paused right away to prevent further damage to your sender score.

• Faster recovery: Early detection means you can resolve the issue faster and restore your deliverability before it hurts your pipeline.

With SmartReach.io, you don’t have to worry about blacklists catching you by surprise, we help you stay ahead and keep your emails on track.

Try SmartReach.io free for 14 days. 

Frequently Asked Questions About Email Blacklisting

Why is my email IP blacklisted?

Your email IP can get blacklisted if it’s linked to spam-like behavior. This can happen due to high bounce rates, spam complaints, sending to bad lists, or if your server is compromised and used to send harmful emails.

How do I remove my email IP from blacklist?

First, find out which blacklist has flagged your IP using tools like MX Toolbox. Fix the issue that caused the blacklisting, such as cleaning your email list or securing your server, then follow that blacklist’s removal process.

What happens if your domain gets blacklisted?

If your domain is blacklisted, your emails may get blocked completely or land in spam folders. This hurts your email deliverability, lowers open rates, and can damage your business reputation.

How do I fix a blacklisted IP domain email?

Identify which blacklist you’re on, fix the root cause (such as authentication issues or poor list hygiene), and submit a removal request. You may also need to warm up your sending reputation again.

How do I un-blacklist my email?

To un-blacklist your email, stop any problematic sending behavior, correct technical issues, and submit a removal request to the blacklist provider. Regular monitoring helps prevent future issues.

What happens if my IP is blacklisted?

Your emails may not reach recipients at all, or they could be sent to spam. This can lead to missed opportunities, lower engagement, and lost revenue.

How to fix a blacklisted email?

Check which blacklist flagged your email. Fix problems like sending to bad lists or using poor content, update your email setup (SPF, DKIM, DMARC), and request removal from the blacklist.

How do I fix my domain blacklist?

Clean up your email practices, secure your systems, and ensure all authentication is correct. Then, submit removal requests and monitor your reputation going forward.