If your emails are not reaching recipients, it may be because your server IP is on a blacklist. In this article, we explain what blacklists are, how to check if you are blocked, and how to get off a blacklist.

What is an email blacklist?

An email blacklist (also known as a blocklist or DNSBL) is a list of IP addresses suspected of sending spam or malware. Mail servers around the world use these lists to filter suspicious emails.

How does it work?

  1. You send an email
  2. The receiving mail server checks if your IP is on known blacklists
  3. If your IP is on a blacklist, your email is rejected or marked as spam

Why do you end up on a blacklist?

The most common causes:

  • Hacked email account - A compromised account sends spam
  • Infected computer/website - Malware sends emails without your knowledge
  • Poorly configured mail server - Missing SPF, DKIM, or DMARC records
  • Open relay - A mail server that allows anyone to send mail
  • Poor sending practices - Too many emails in a short time, purchased mailing lists
  • Shared IP - Another user on the same server IP behaves poorly
  • Spam complaints - Recipients mark your legitimate mail as spam

Check your IP against blacklists

Step 1: Find your mail server IP

You need to know which IP address your mail server uses:

Via terminal (Mac/Linux):
nslookup -type=mx yourdomain.nl

Via online tool:
Go to MXToolbox.com and enter your domain.

Step 2: Check for blacklists

There are various free tools to check if your IP is on a blacklist:

MXToolbox Blacklist Check:
1. Go to mxtoolbox.com/blacklists.aspx
2. Enter your IP address or domain
3. Click on "Blacklist Check"
4. The tool checks dozens of blacklists at once

MultiRBL.valli.org:
1. Go to multirbl.valli.org
2. Enter your IP
3. View the results from 200+ blacklists

Other popular tools:
- Spamhaus Lookup: spamhaus.org/lookup
- Barracuda: barracudacentral.org/lookups
- SURBL: surbl.org

What to do if you are blocked

Step 1: Identify the cause

Before you request delisting, you need to find and resolve the cause:

Check for compromised accounts:
1. Log in to DirectAdmin
2. Go to "Email Manager" > "Email Queue"
3. Check if there are large amounts of outgoing mail in the queue
4. Check which email account is sending the messages

Check your website for malware:
1. Scan your website with tools like Sucuri SiteCheck
2. Look for suspicious files or code
3. Check your server logs for suspicious activity

Check your DNS records:
1. Do you have an SPF record?
2. Is DKIM configured?
3. Consider adding DMARC

Step 2: Resolve the issue

Depending on the cause:

Compromised account:
- Immediately change the password
- Enable 2FA if possible
- Check for any unknown forwarding rules

Infected website:
- Remove the malware
- Update all software (CMS, plugins, themes)
- Change all passwords

DNS issues:
- Add a correct SPF record
- Configure DKIM signing
- Implement DMARC

Step 3: Request delisting

Each blacklist has its own delisting procedure. Here are the main ones:

Spamhaus:
1. Go to spamhaus.org/lookup
2. Enter your IP
3. If you are listed, click on the listing
4. Follow the instructions for delisting
5. You must prove that the issue is resolved

Spamcop:
1. Go to spamcop.net
2. Spamcop automatically removes listings after 24 hours without new complaints
3. Resolve the issue and wait

Barracuda:
1. Go to barracudacentral.org/lookups
2. Look up your IP
3. Click on "Request Removal"
4. Fill out the form

SORBS:
1. Go to sorbs.net
2. Use their lookup tool
3. Follow the delisting instructions (often a small fee)

Microsoft/Outlook.com:
1. Go to sender.office.com
2. Register your IP/domain
3. Submit a delisting request

Prevention: Avoid future blacklisting

Best practices for email sending

Set up authentication correctly:
- SPF: Specify which servers may send mail on your behalf
- DKIM: Digital signature for your emails
- DMARC: Policy for how recipients should handle failed authentication

Healthy sending practices:
- Only send to people who have opted in
- Process unsubscribes within 10 days
- Keep your bounce rate below 2%
- Keep spam complaints below 0.1%

Technical measures:
- Use strong passwords for all email accounts
- Enable 2FA where possible
- Limit the number of emails per hour/day
- Monitor your outgoing mail queue

Regularly check

Set a reminder to check your IP against blacklists monthly. This way, you can discover problems before they have a significant impact.

Frequently asked questions

"How long does delisting take?"

This varies by blacklist:
- Some are automatic within 24-48 hours after resolving the issue
- Others require manual review and can take 1-7 days
- Spamhaus can take up to 2 weeks in severe cases

"I am on a blacklist but do not send spam"

This can be due to:
- Another user on the same shared IP
- A hacked account without your knowledge
- Your IP has been abused by someone else in the past

"Should I address all blacklists?"

Focus on the most important ones:
1. Spamhaus - Most influential
2. Barracuda - Many business users
3. Microsoft - For Outlook.com/Hotmail recipients
4. Google - For Gmail recipients

Smaller blacklists often have less impact.

"Can I get a new IP?"

Sometimes this is an option, but:
- It does not solve the underlying problem
- The new IP may also have a bad reputation
- It is better to fix the issue

Monitoring and prevention tools

Free monitoring

  • Google Postmaster Tools: Insight into your reputation with Gmail
  • Microsoft SNDS: Smart Network Data Services for Outlook
  • MXToolbox Monitor: Free monitoring of your domain
  • SendGrid: Email delivery service with built-in reputation management
  • 250ok: Comprehensive email deliverability monitoring
  • GlockApps: Test inbox placement and blacklist monitoring

Need help?

We are here for you! Are you facing any issues or do you have questions? Our support team is happy to assist you personally. Send us a message via the ticket system - we usually respond within a few hours and are happy to help.