Your emails stop arriving. Customers say they never got the invoice, quotes bounce back with a cryptic error, and the messages that do get through land in spam. Then you find the reason: your mail server, or your domain, is on a blacklist.
For a business that runs on email, this is a serious problem, and it can happen without you sending a single bad message yourself. This guide explains what a blacklist is, how to check whether you’re on one, how to get removed and, most importantly, how to find and fix the cause so you don’t end up back on it.
What Is an Email Blacklist?
An email blacklist, also called a blocklist or DNSBL, is a database of IP addresses and domains that have been linked to spam, phishing or other abuse. Mail providers and spam filters check these lists in real time. If your sending IP or domain appears on a list they trust, they may reject your mail outright, send it to spam or throttle it heavily.
There isn’t one master list. Dozens exist, run by different organisations with different rules, and different receivers trust different lists. Some, like Spamhaus, carry great weight and are used by a large share of the world’s mail systems. Others are small and rarely matter. This is why you can be blocked by some recipients and not others, which makes the problem confusing to diagnose.
Why Mail Servers Get Blacklisted
Listings aren’t random. They follow from something your server was seen doing. The most common causes are:
- A compromised website or mail account. A hacked WordPress site or a stolen mailbox password lets attackers send spam or phishing through your server. This is the most common cause we see, and the owner often has no idea it’s happening.
- A compromised server or account on shared infrastructure. If another customer on your IP is sending spam, your reputation can suffer with theirs.
- Spam complaints. Recipients marking your mail as spam builds a poor sender reputation, even for legitimate marketing.
- Poorly managed mailing lists. Sending to old, purchased or unconfirmed addresses generates bounces and spam-trap hits.
- Missing or broken authentication. Without proper SPF, DKIM and DMARC records, your mail looks forgeable, and attackers can spoof your domain.
- A bad IP history. Sometimes the IP was previously used by a spammer before you got it.
- Open relays or misconfigured servers that let anyone send through them.
If your listing appeared suddenly, check for a compromise first. A site hack and a blacklisting often arrive together, which is why our guide on what to do in the first hour of a WordPress hack lists blocked email as a warning sign.
Step 1: Confirm You’re Actually Blacklisted
Don’t assume. Start by reading the bounce message, because it often names the list or gives a code and a link. Then check your sending IP and domain against a blacklist lookup tool. Several free multi-list checkers exist, and the major lists such as Spamhaus provide their own lookup pages.
Note the exact list or lists you appear on, the reason given and the IP or domain affected. You’ll need all three, because each list has its own removal process and requirements.
Step 2: Find the Cause Before You Ask for Removal
This is where most people go wrong. Requesting delisting without fixing the cause rarely works, and if it does, you’ll be relisted quickly, sometimes with a harsher penalty.
Check these in order:
- Scan your website and server for malware. Look for web shells, injected scripts and unfamiliar scheduled tasks that could be sending mail.
- Review your mail queue and logs. A queue full of messages you didn’t write is a clear sign of abuse. Look at which account or script is sending them.
- Check your mailboxes for compromise. Look for forwarding rules you didn’t create, unfamiliar logins and unusually high sending volume.
- Review your contact forms and plugins. Spammers often abuse unprotected forms to relay mail.
- Verify your authentication records (covered below).
If you find signs of a hack, work through the containment steps in our guide first. A compromised site that’s still active will simply get you relisted. And as we explain in our post on why restoring a backup doesn’t fix a hacked website, the entry point must be closed or the problem returns.
Step 3: Fix the Underlying Problem
Once you’ve found the cause, remove it properly:
- Clean the infection and close the entry point, then reset every credential the attacker could have reached, including mailbox passwords.
- Clear the spam from the mail queue so it isn’t delivered after you’ve fixed the cause.
- Remove malicious forwarding rules and rogue accounts.
- Update and patch your website software and delete anything unused.
- Secure your forms with proper validation or CAPTCHA so they can’t be used as relays.
- Clean your mailing lists. Remove bounced, inactive and unconfirmed addresses.
Step 4: Set Up Email Authentication Correctly
Authentication proves that mail claiming to be from your domain really is. Receivers increasingly require it. Gmail, Yahoo and Microsoft have all tightened their expectations for senders, particularly for bulk mail, and missing authentication is a common reason legitimate mail ends up in spam.
You need three things:
SPF lists the servers allowed to send mail for your domain. Keep it accurate and avoid the common mistake of exceeding the limit on DNS lookups, which causes SPF to fail.
DKIM adds a cryptographic signature to each message so receivers can verify it wasn’t altered and really came from you.
DMARC tells receivers what to do when SPF or DKIM fail, and sends you reports. Start with a monitoring policy so you can see who is sending as your domain, then move to quarantine or reject once everything legitimate is passing.
Also check that your sending IP has a reverse DNS (PTR) record matching your mail server’s hostname. Many receivers reject mail without one.
Step 5: Request Delisting
Only now should you ask to be removed. Each list has its own process, and the details differ, so follow the instructions on that list’s own site.
A few general principles apply:
- Use the list’s official removal form. Never pay anyone who promises guaranteed removal, and be wary of lists that charge for delisting.
- Explain what happened and what you fixed. A short, specific, honest statement helps. Vague requests get ignored.
- Expect different timelines. Some lists remove you automatically after a period without abuse. Others require manual review.
- Understand the type of listing. Some lists, such as policy lists covering dynamic or residential IP ranges, aren’t about your behaviour at all. Those are removed through your internet provider or hosting company rather than by appeal.
- Be patient with repeat listings. If you’ve been listed before, expect stricter handling.
Reputation with the large mailbox providers also matters separately from blacklists. If Gmail or Microsoft are still sending your mail to spam after you’re delisted, their own postmaster tools show how they rate your domain and IP.
Step 6: Recover Your Reputation
Delisting removes the block, but your sender reputation takes longer to rebuild. For the next few weeks:
- Send only to engaged recipients and keep volume steady rather than sending large bursts.
- Monitor bounce rates and complaints closely.
- Watch the blacklist status of your IP and domain regularly.
- Review your DMARC reports to catch anyone else sending as your domain.
How to Stay Off Blacklists
Most listings are preventable. The habits that keep you off:
- Keep your website and server software updated, and delete unused plugins.
- Use strong, unique mailbox passwords with two-factor authentication where possible.
- Configure SPF, DKIM and DMARC properly and keep them current.
- Monitor your mail queue for unusual volume.
- Only email people who’ve agreed to hear from you, and make unsubscribing easy.
- Put a web application firewall in front of your site to cut off a common route for attackers.
On that last point, be realistic. A firewall reduces your exposure by blocking attacks it can see, but it doesn’t patch a vulnerable plugin and can’t clean a server that’s already sending spam. Protection and cleanup are separate jobs, and you need both.
Get Help Now: Armor SOS
If your mail server is blacklisted and you suspect a compromise, Armor SOS is Tremhost’s emergency cleanup service. Triage is free and usually starts the same day. We contain the attacker’s access, find and remove whatever was sending the mail, reset compromised credentials, handle your Google and blacklist delisting, and give you a written report on how they got in. We work on sites hosted anywhere, and developers can use us behind their own name, since we never contact your client.
Make Sure It Doesn’t Happen Again: Armor Shield
If your site takes payments or holds client data, the smartest follow-up is Armor Shield, at $29 per site per month. It includes firewall rules written for your specific application, unlimited malware cleanup if you’re ever compromised again, Google and blacklist delisting handled by us, a monthly report and a named engineer with a four-hour response. It costs less than a single emergency cleanup.
For simpler informational sites, Armor Guard gives you the firewall, DDoS protection and SSL for $9 a month. Cleanup is quoted separately on that plan.
Frequently Asked Questions
How do I know if my email server is blacklisted?
Check the bounce messages for a list name or error code, then run your sending IP and domain through a blacklist lookup tool. Major lists such as Spamhaus also offer their own lookup pages.
Why did my email server get blacklisted?
Common causes are a compromised website or mailbox sending spam, spam complaints, poor mailing list hygiene, missing email authentication, a bad IP history or a misconfigured server. A hacked site is the cause we see most often.
How do I remove my IP from a blacklist?
Find and fix the cause first, then use the list’s official removal process and explain what you fixed. Requesting removal before fixing the problem usually fails or leads to relisting.
How long does delisting take?
It varies by list. Some remove you automatically after a clean period, while others review requests manually. Listings caused by an unresolved compromise can keep returning until the cause is fixed.
Should I pay a service to get me delisted?
Be cautious. Legitimate lists provide official removal forms, and anyone guaranteeing removal for a fee deserves suspicion. Fixing the cause matters more than any paid service.
Can a hacked website get my email blacklisted?
Yes. Attackers commonly use compromised sites and server accounts to send spam or phishing, which damages your IP and domain reputation.
Do I need SPF, DKIM and DMARC?
Yes. Receivers increasingly expect all three, and missing or broken authentication is a common reason legitimate mail lands in spam or gets rejected.
Why is my email still going to spam after I was delisted?
Delisting removes the block, but your sender reputation takes time to rebuild. Check authentication, send only to engaged recipients and watch your reputation in the major mailbox providers’ postmaster tools.
How much does it cost to fix a blacklisted server?
With Tremhost, triage is free and cleanup is quoted after we see what we’re dealing with. On Armor Shield, cleanup and delisting are included at no extra charge, every time.
