Revenue dropped overnight. Your transactional emails — password resets, invoices, order confirmations — aren't reaching customers. Support tickets start piling up. Someone on your team runs a quick check and finds it: your sending IP or domain is on a blacklist.
This is one of the fastest ways a business loses money without touching a single line of code.
Getting blacklisted is not rare. It happens to legitimate businesses constantly — often because of a single misconfigured record, a compromised account, or a spike in bounce rates after a list import. The good news: most blacklistings are reversible. The bad news: if you don't fix the root cause first, you'll be back on the list within days.
This guide covers how to find which list you're on, how to get off each major one, and how to make sure it doesn't happen again.
What Email Blacklists Actually Are
A blacklist (technically a DNSBL — DNS-Based Blackhole List) is a real-time database of IP addresses and domains known or suspected to send spam. Mail servers query these lists during the SMTP handshake. If your sending IP appears in a lookup, the receiving server either rejects the message outright or sends it to spam.
There are over 100 active public blacklists. The major ones query billions of IPs daily. Some are aggressive and list IPs pre-emptively. Others require sustained spam behavior before listing. A few are pay-to-delist scams with little legitimate use.
The critical distinction: IP-based blacklists block your sending server's address. Domain-based blacklists block your domain regardless of which IP it sends from. You can be on both at once.
How You Got On the List
Before submitting a single removal request, understand why you were listed. Delisting without fixing the cause gets you relisted within 24–72 hours.
High bounce rate
Sending to a large number of invalid addresses is the fastest path to a blacklist. Spam traps — addresses maintained by blocklist operators that should receive zero legitimate email — are seeded into purchased lists and old, unvalidated databases. Hit enough of them and listing is automatic.
Sudden spike in sending volume
Sending 500 emails a day for a year and then blasting 50,000 in an afternoon looks exactly like a compromised account. Receiving servers notice. So do blocklist monitors.
Compromised sending account or server
If someone unauthorized sent from your IP or domain, you may be listed for spam you never authorized. Check your email provider's sent log before assuming this isn't the case.
Missing or broken SPF, DKIM, or DMARC
Unauthenticated email is treated with deep suspicion. Many blocklists factor in authentication failures before listing. Some list you for authentication failures alone. If your SPF record is missing or malformed, this may be the proximate cause.
Shared IP reputation bleed
If you're on a shared IP from an ESP (email service provider) and a neighboring sender on that IP goes rogue, you inherit their reputation problems. This is an argument for dedicated sending IPs on high-volume sends.
Step 1: Find Out Which Lists You're On
Don't guess. Check all of them at once.
MXToolbox Blacklist Check — checks your IP against 100+ DNSBLs simultaneously:
https://mxtoolbox.com/blacklists.aspx
Enter your sending IP address (not your domain). For your domain reputation, also check:
https://mxtoolbox.com/domain/{yourdomain.com}
Talos Intelligence — Cisco's reputation database, used by a large share of enterprise mail filters:
https://talosintelligence.com/reputation
Sender Score — a 0–100 score based on your sending IP's historical behavior:
https://www.senderscore.org/
Google Postmaster Tools — if Gmail is rejecting your mail specifically, this shows your domain and IP reputation from Google's perspective:
https://postmaster.google.com/
From the command line — check a specific DNSBL manually by reversing your IP octets and querying the list:
# For IP 192.0.2.1, query Spamhaus SBL:
dig 1.2.0.192.zen.spamhaus.org A
# A response (non-NXDOMAIN) means you're listed.
# NXDOMAIN means you're clean on that list.
The zen.spamhaus.org zone combines Spamhaus SBL, XBL, and PBL into one query. It's the most important single check.
Run these before doing anything else. You need a complete picture of where you're listed before you start submitting removal requests.
Step 2: Fix the Root Cause First
This is non-negotiable. Every major blacklist operator checks whether the spam behavior is still active before approving a removal request. If you delist and the problem is still live, you get automatically relisted — sometimes with a longer cooldown.
Validate your sending lists. Remove hard bounces immediately. Purge addresses that haven't engaged in 12+ months. Do not send to purchased or scraped lists.
Check your authentication records:
# SPF
dig TXT yourdomain.com | grep spf
# DMARC
dig TXT _dmarc.yourdomain.com
# DKIM (replace selector1 with your actual selector)
dig TXT selector1._domainkey.yourdomain.com
If any of these return nothing, that's a problem to fix before delisting. Receiving servers running reputation checks look at whether your authentication is in place.
Audit your sending infrastructure for compromise. Check your ESP's activity log for sends you didn't initiate. Rotate API keys and credentials if anything looks unfamiliar.
Lower your sending volume temporarily. If you triggered listing through a volume spike, bring your daily send count back to your historical baseline while you resolve the issue.
Step 3: Submit Removal Requests — List by List
Each blacklist operator runs their own delisting process. There is no single form that covers all of them. Here are the major ones you're likely to encounter.
Spamhaus (SBL, XBL, PBL, DBL)
Spamhaus is the most impactful blocklist in email. Being listed here causes rejections at a large percentage of enterprise mail servers.
SBL (Spamhaus Block List) — manually maintained, lists known spam sources. Removal requires explaining the spam activity and demonstrating it's resolved. No self-service removal.
https://www.spamhaus.org/lookup/
XBL (Exploits Block List) — lists IPs running exploits, open proxies, or malware. If you're on XBL, your server is compromised. Clean the server first, then request removal.
PBL (Policy Block List) — lists IP ranges that should not be sending outbound email directly (dynamic IPs, residential ranges). If you're a legitimate business on a static IP, you can request removal here:
https://www.spamhaus.org/pbl/removal/
DBL (Domain Block List) — lists domains found in spam. Removal requires contacting Spamhaus directly and demonstrating cleanup.
Spamhaus is thorough. Expect 24–72 hours for a response and provide specific detail about what changed.
Barracuda Networks (BRBL)
Barracuda's list is widely used by enterprise mail gateways. Self-service removal is available but requires you to submit a lookup first and accept their terms:
https://www.barracudacentral.org/lookups
Click "Request Removal" after the lookup. Barracuda typically processes requests within 12 hours.
SORBS (Spam and Open Relay Blocking System)
SORBS lists spam sources, open relays, and compromised hosts. They have a zone-specific removal process:
https://www.sorbs.net/cgi-bin/lookup.cgi
SORBS requires you to demonstrate the problem is resolved and sometimes asks for a fee for faster processing. Their free removal process can take several days.
SpamCop (SCBL)
SpamCop's list is time-limited — listings expire automatically after 24 hours if no new spam is detected. If you're on SpamCop, the fastest fix is to stop all spam-like behavior and wait for auto-expiry. Attempting manual removal before expiry rarely accelerates the timeline.
Check your status:
https://www.spamcop.net/bl.shtml
Microsoft SNDS and Junk Mail Reporting
If Outlook and Hotmail are rejecting your mail, Microsoft runs its own reputation system:
https://sendersupport.olc.protection.outlook.com/pm/troubleshooting.aspx
Register your IP with the Smart Network Data Services (SNDS) program to see how Microsoft's filters are classifying your mail. If you're blocked, submit a delist request through the form above.
Google Postmaster
Google doesn't operate a traditional blacklist. Gmail filtering is reputation-based. If your domain reputation is "Bad" in Postmaster Tools, you're being downgraded across Gmail — not formally listed, but effectively blacklisted.
Fix: warm up slowly with engaged recipients, fix authentication, reduce complaint rates. There is no removal form because there's no formal listing.
Removal Request Template
When emailing a blocklist operator directly, be specific. Vague requests get ignored.
Subject: Delisting Request — [Your IP or Domain] — [List Zone]
To the [Blocklist Name] team,
We are writing to request removal of [IP address / domain] from [specific zone].
We identified the listing on [date] through [tool used]. After investigation,
the root cause was [specific cause: compromised account / bounce rate spike /
misconfigured relay / etc.].
Actions taken:
- [Specific fix 1 — e.g., "Removed 4,200 invalid addresses from sending list"]
- [Specific fix 2 — e.g., "Rotated SMTP credentials and audited API access"]
- [Specific fix 3 — e.g., "SPF record updated to include all sending services"]
We have verified that no unauthorized sending has occurred since [date].
Spam trap hit rate has dropped to [0 / negligible].
We request removal from the listing and commit to continued compliance with
your listing criteria.
[Name, company, contact email]
What Breaks When You Rush This
Relisting within 48 hours. The single most common outcome of submitting removal without fixing root cause. Most major lists track relisting patterns and may extend your cooldown period on the second listing.
Getting flagged as a repeat offender. Spamhaus and Barracuda note repeated removal requests against the same IP. A pattern of listing → removing → relisting → removing signals an operator who isn't serious about cleanup, and removal approval gets harder.
Email provider account suspension. If you're using SendGrid, Postmark, or AWS SES and your account generates enough complaints or spam trap hits, the provider may suspend your account independently of any blacklist. This is a harder problem than a DNSBL listing.
Missing secondary listings. Fixing the main Spamhaus listing but missing the Barracuda listing means the problem persists for a subset of your recipients. Always run a full check across all lists before declaring the issue resolved.
Preventing the Next Listing
Monitor your IP and domain continuously
Manual checks are reactive. By the time you notice a blacklisting, you've already missed potentially thousands of transactional emails. Tools like ZeroHook monitor your IP and domain against 50+ blacklists in real time and alert you within minutes of a new listing — before your support tickets start piling up.
Keep bounce rates below 2%
This is the industry threshold most ESPs and receiving servers use as a signal of a healthy list. Above 2%, you're in warning territory. Above 5%, you're in spam folder territory and approaching automatic listing range on the aggressive blocklists.
Implement email list hygiene on a schedule
Purge hard bounces after every send. Suppress addresses with no engagement in the last 12 months. Use double opt-in for new subscribers. Run your list through a validation service before any large campaign.
Authenticate your domain properly
SPF, DKIM, and DMARC together signal that your domain is controlled and your email is legitimate. Without them, every send carries a higher spam score. With a p=reject DMARC policy in place, even a compromised sending account can't spoof your domain.
Use dedicated sending IPs for high-volume sends
Shared IPs from ESPs are cost-effective but expose you to your neighbors' reputation. At sufficient volume (generally 50,000+ emails/month), a dedicated IP with a controlled warmup period gives you a clean reputation baseline that you own.
The Blacklist Monitoring Checklist
Run this after resolving any listing, and on a monthly basis as maintenance:
# 1. Check Spamhaus combined zone
dig {reversed-ip}.zen.spamhaus.org A
# 2. Verify SPF record is valid and under 10 DNS lookups
dig TXT yourdomain.com | grep spf
# 3. Verify DMARC policy is at minimum p=quarantine
dig TXT _dmarc.yourdomain.com
# 4. Check domain reputation via MXToolbox
# https://mxtoolbox.com/blacklists.aspx
# 5. Check Google Postmaster domain reputation
# https://postmaster.google.com/
# 6. Verify PTR (reverse DNS) record matches your sending hostname
dig -x {your-sending-IP}
TL;DR
- Check all lists first — MXToolbox, Talos, Spamhaus, Barracuda, and Google Postmaster before submitting any removal requests
- Fix the root cause before delisting — high bounce rate, missing SPF/DKIM/DMARC, or a compromised account. Delisting without fixing gets you relisted within 48 hours
- Submit list-specific removal requests — each blocklist (Spamhaus, Barracuda, SORBS, SpamCop, Microsoft) has its own process; there is no universal form
- Be specific in your removal requests — document what caused the listing and what you changed
- Set up continuous monitoring — manual checks are too slow; automated blacklist monitoring closes the gap between listing and detection
- Treat email list hygiene as infrastructure — bounce rates, spam trap hits, and engagement patterns all feed the reputation systems that get you listed in the first place
*Part of an ongoing series on email deliverability and DNS security.
