How to Check If You're Blacklisted and Get Delisted

What This Error Means

Email blacklists (DNSBLs — DNS-based Blackhole Lists, defined in RFC 5782) are databases of IP addresses known to send spam or be associated with malicious activity. If your sending IP appears on a major blacklist, receivers automatically reject or spam-filter your email during the RFC 5321 SMTP transaction. The fix: identify the root cause, resolve it, request delisting, and set up monitoring to prevent recurrence.

There are over 100 active blacklists, but not all carry the same weight. Major email providers primarily check the well-known lists (Spamhaus, Barracuda, SpamCop, SORBS), while smaller or regional providers may check additional lists. A single listing on Spamhaus can block your email to the majority of mailboxes worldwide.

Why It Matters

Being listed on a blacklist causes immediate deliverability problems:

How to Check Your Blacklist Status

Using the mxio Blacklist Check

Use the mxio Blacklist Check with your sending IP address. The tool checks your IP against dozens of active blacklists in parallel and shows:

• Which lists you appear on (if any)
• The severity of each listing
• Links to delisting pages where available

Finding Your Sending IP

If you are not sure which IP to check:

1. Check the first external Received hop in a recent sent message header — this shows the IP the receiving server saw
2. Review your outbound SMTP logs or your email provider's documentation for your sending IP
3. If you manage your own mail server, run an mxio MX Lookup on your domain — but note that MX records point to inbound servers, which may use different IPs than your outbound SMTP path

For cloud-hosted email (Google Workspace, Microsoft 365), you are on shared infrastructure and do not control the IP directly — the provider manages blacklist issues for their IP pools.

Why You Were Listed

Understanding the root cause is essential. Delisting without fixing the underlying problem means you will be re-listed, often with a longer hold time.

Common Causes

Compromised account: An email account on your server was compromised (weak password, phished credentials) and used to send spam. This is the single most common cause.

Open relay: Your mail server accepts and forwards email from anyone, not just authorized users. Spammers exploit open relays to send massive volumes.

Malware or botnet: A machine on your network is infected and sending spam without your knowledge.

No or poor PTR record: Missing reverse DNS signals to blacklists that the IP is not a legitimate mail server.

Sudden volume spike: Dramatically increasing your sending volume (e.g., during a marketing campaign) from an IP with no sending history triggers automatic listings.

Shared IP issues: On a shared hosting provider or shared email platform, another customer's bad behavior gets the entire IP range listed.

How to Get Delisted

Step 1: Fix the Root Cause

Before requesting delisting, fix whatever caused the listing. If you delist without fixing the problem, you will be re-listed — often with a longer hold time or manual review requirement.

For compromised accounts:

• Force password resets on all affected accounts
• Enable two-factor authentication
• Check for mail forwarding rules added by the attacker
• Review sent mail logs for the scope of the spam

For open relays:

• Configure your mail server to only accept mail from authenticated users
• Block port 25 outbound from all machines except your mail server
• Test with online open relay checkers

For malware:

• Scan all machines on your network
• Check for unusual outbound connections on port 25
• Block outbound SMTP from all hosts except your designated mail server

For a comprehensive recovery process, see the Blacklist Recovery Guide.

Step 2: Request Delisting

Each blacklist has its own delisting process:

Spamhaus:

• Visit check.spamhaus.org
• Enter your IP and view listing details
• Follow the removal process (automated for most listings)
• SBL listings require manual review; CBL/XBL are typically automated

Barracuda (BRBL):

• Visit barracudacentral.org/lookups
• Submit a removal request with your IP
• Include steps you have taken to resolve the issue
• Usually processed within 12-24 hours

SpamCop:

• Listings auto-expire after 24-48 hours if spam reports stop
• No manual delisting process — fix the issue and wait
• Check status at spamcop.net

SORBS:

• Visit sorbs.net
• Follow their delisting process (varies by list type)
• Some SORBS lists require a nominal donation for expedited removal

UCEPROTECT:

• Level 1: Auto-expires after 7 days if no new spam detected
• Level 2 & 3: Entire IP blocks — contact your ISP/hosting provider
• Manual removal available for a fee (controversial)

Step 3: Verify and Monitor After Delisting

After successfully delisting:

• Run the mxio Blacklist Check to confirm the listing is cleared
• Monitor your IP daily for the first week
• Check weekly for the first month
• Set up automated monitoring for ongoing protection

Prevention and Ongoing Monitoring

Blacklisting is not a one-time event. IPs get re-listed, shared infrastructure introduces new risks, and compromised accounts happen without warning. Ongoing monitoring catches listings before they cause delivery failures.

Best Practices

• Enforce strong passwords and 2FA for all email accounts
• Keep software patched — mail servers, web applications, operating systems
• Rate limit outbound email to detect unusual spikes early
• Use dedicated IPs for email if possible (avoid shared IP pools)
• Maintain valid PTR records for all sending IPs
• Send from consistent IPs — do not rotate sending IPs unnecessarily
• Warm up new IPs gradually when migrating to new infrastructure

Monitoring Checklist

• Check sending IPs against major blacklists weekly (or use automated monitoring)
• Review mail server logs for unusual patterns
• Monitor DMARC aggregate reports for unauthorized sending sources — see Why Is DMARC Failing? for details
• Track bounce rates — sudden increases indicate a listing
• Review spam complaint rates in your email platform

Set up domain health monitoring to catch blacklist events the moment they happen — before they affect deliverability. mxio checks your sending IPs against major DNSBLs continuously and alerts you immediately when a listing is detected.

Blacklist-Specific Guides

Each blacklist has its own removal process. See our detailed guides:

Most impactful:

• Spamhaus — multiple lists (SBL, XBL, PBL, ZEN, DBL, CSS), highest deliverability impact
• Barracuda — manual removal request, 12-24 hours
• Abusix — combined intelligence, enterprise-grade

Widely used:

• SpamCop — auto-delists in 24 hours
• 0spam — auto-delists in 24 hours, 1M+ servers
• Invaluement — targets snowshoe spam, used by MailRoute

Domain-based:

• SURBL — domains in spam, auto-removes when clean
• URIBL — domains in spam, auto-removes when clean

Specialized:

• Lashback UBL — suppression list abuse detection
• Backscatterer — misdirected bounce detection
• DroneBL — compromised hosts and botnets
• BLOCKLIST.DE — attack IPs (brute force, exploits)
• SpamEatingMonkey — auto-expires in 7 days
• Truncate/GBUdb — fully automated, no manual removal

Minor / Unreliable:

• SpamRats — dynamic IP focus, requires valid rDNS
• PSBL — auto-expires in 2-3 weeks
• UCEProtect Level 1 — auto-removes in 7 days (pay-to-expedite — don't pay)
• UCEProtect Level 2 — lists entire /24 ranges, wait 7 days, don't pay
• UCEProtect Level 3 — lists entire ASNs, wait 7 days, don't pay

Related Issues

• Microsoft 365 Error 550 5.7.708 — IP blocked by Exchange Online Protection
• Emails Going to Spam — Blacklisting is a major cause of spam filtering
• Missing PTR Record — Missing reverse DNS contributes to listings
• Blacklist Recovery Guide — Complete recovery process for severe listings