SORBS Blacklist: Checking and Delisting Guide

Understanding SORBS

SORBS (Spam and Open Relay Blocking System) is one of the older blacklists, established in 2001. It was acquired by Proofpoint (now part of Thoma Bravo portfolio) and continues to operate.

SORBS organizes listings into multiple zones, each targeting different abuse types:

Zone	What It Means
spam	Direct spam sending
http	Web-based spam
smtp	Open relay abuse
dul/duhl	Dynamic/residential IPs
recent	Recent spam activity
old	Historical spam activity
zombie	Compromised systems

Checking Your Status

SORBS direct lookup

Go to sorbs.net and use their lookup tool.

Enter your IP to see:

• Whether you're listed
• Which zone(s)
• Listing details

MXToolbox

Go to mxtoolbox.com/blacklists.aspx

MXToolbox checks SORBS along with 100+ other lists.

SORBS Impact in 2026

The reality:

SORBS is less impactful than it was years ago:

• Gmail: Doesn't heavily weight SORBS
• Outlook: Uses other signals primarily
• Yahoo: May check but not decisive
• Enterprise: Some still use SORBS in filtering

A SORBS listing is worth fixing but isn't an emergency like Spamhaus.

Practitioner note: When clients panic about SORBS listings, I tell them to check Spamhaus first. A Spamhaus listing is a deliverability crisis. SORBS is more of an inconvenience that some mail servers care about and many don't.

Delisting Process

Auto-expiring zones

Some SORBS zones automatically expire:

• recent — Expires ~48-96 hours after spam stops
• zombie — May expire after cleanup detected

If you fixed the issue, wait a few days and check again.

Manual removal zones

Other zones require removal requests:

1. Go to sorbs.net/overview.shtml (or their support page)
2. Find the delist/removal section
3. Submit request with your IP
4. Explain what caused the listing
5. Describe what you've fixed

SORBS has had variable responsiveness over the years. Expect days to weeks for manual removal.

DUHL (Dynamic User/Host List)

The DUHL zone lists dynamic and residential IPs. This is policy-based, similar to Spamhaus PBL.

If you're on DUHL:

• Your IP is dynamic/residential
• Direct mail sending isn't expected
• Use proper mail relay instead
• Removal may not be possible

Common SORBS Scenarios

Listed on "spam" zone

Cause: Your IP sent spam or appeared in spam reports

Fix:

1. Identify spam source (malware, bad list, etc.)
2. Stop the spam
3. Wait for auto-expiration or request removal
4. Implement better practices

Listed on "smtp" zone

Cause: Open relay detected or suspected

Fix:

1. Verify mail server isn't an open relay
2. Secure SMTP configuration
3. Request removal
4. Test relay status

Listed on "dul" zone

Cause: Dynamic/residential IP range

Fix:

• Use mail relay through ISP
• Use ESP for sending
• Don't try to delist (it's policy)

Listed on "recent" zone

Cause: Recent spam activity

Fix:

1. Fix the underlying issue
2. Wait 48-96 hours
3. Check for auto-removal
4. Request if not auto-removed

When to Worry About SORBS

Worry if:

• Sending to enterprises that use SORBS
• Multiple blacklist appearances
• Consistently blocked by specific recipients
• SORBS is part of larger reputation problem

Don't panic if:

• Gmail/Outlook delivery is fine
• Only listed on SORBS, not Spamhaus
• Consumer email is your primary audience
• Listing is in auto-expiring zone

SORBS vs Other Blacklists

List	Impact	Delisting
Spamhaus	Critical	Manual request
Barracuda	High (enterprise)	Manual request
SORBS	Moderate	Auto or manual
SpamCop	Moderate	Auto (24 hours)
URIBL	Domain-level	Contact

SORBS falls in the "moderate impact" category. Important for enterprise delivery, less critical for consumer.

Prevention

To avoid future SORBS listings:

List hygiene

• Remove unengaged subscribers
• Validate addresses
• Never use purchased lists

Infrastructure security

• No open relays
• Keep systems patched
• Monitor for compromise

Sending practices

• Proper warmup
• Low complaint rates
• Honor unsubscribes

Use proper infrastructure

• Don't send from dynamic IPs
• Use static IPs with reverse DNS
• Consider ESP for simplicity

Proofpoint Ownership

SORBS is now part of Proofpoint's portfolio. This means:

• Data feeds into Proofpoint products
• Some enterprise users get enhanced SORBS data
• The list continues to be maintained
• Removal processes may change

If you use Proofpoint products, SORBS listings may have additional relevance.

When to Get Help

Consider professional help if:

• Multiple blacklist appearances
• Can't identify listing cause
• Manual removal requests ignored
• Delivery problems persist after delisting

If you're dealing with multiple blacklist issues affecting your sending, schedule a consultation. I'll help systematically address all reputation problems.

Sources

• SORBS: Official Site
• MXToolbox: Blacklist Check
• Proofpoint: Threat Intelligence

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v1.0 · March 2026