Published April 26, 2026 · 12 min read
Enter any domain to check SPF, DKIM, DMARC, MTA-STS, and BIMI configuration — common causes of blacklisting.
Free Domain Check →If your emails are landing in spam or bouncing entirely, one of the first things to investigate is whether your domain or IP address has been blacklisted. Email blacklists (also called DNSBLs — DNS-based Block Lists) are databases that mail servers check before accepting incoming email. If you're on one, your deliverability tanks.
This guide covers: how to check if your domain is blacklisted, the most common blacklists, why domains get listed, how to delist, and how to prevent it happening again.
An email blacklist is a real-time database of IP addresses and domains that have been reported for sending spam, phishing, or abusive email. Mail servers like Gmail, Outlook, and Yahoo query these lists before deciding whether to accept, quaratine, or reject your messages.
There are two types:
Our free mailcheck tool scans your domain's SPF, DKIM, DMARC, MTA-STS, TLS-RPT, and BIMI configuration. While it doesn't query blacklists directly, it identifies the DNS misconfigurations that cause blacklisting — which is more actionable, because fixing these prevents future listings.
curl https://korpo.pro/api/v1/check/yourdomain.com
Returns a 0-100 deliverability score with specific issues flagged.
You can check the most common blacklists using dig or nslookup. To check if an IP is listed, reverse the octets and append the blacklist domain:
# Check IP 198.51.100.22 against Spamhaus dig 22.100.51.198.zen.spamhaus.org TXT # Check IP against SORBS dig 22.100.51.198.dnsbl.sorbs.net TXT # Check IP against Barracuda dig 22.100.51.198.b.barracudacentral.org TXT
If you get a A record back (usually 127.0.0.x), the IP is listed. The TXT record explains why.
For domain-based listings (like Spamhaus DBL and URIBL):
# Check domain against Spamhaus DBL dig yourdomain.com.dbl.spamhaus.org A # Check domain against SURBL/URIBL dig yourdomain.com.multi.uribl.com A
Several free services check your IP/domain against 100+ blacklists simultaneously:
| Blacklist | Type | Impact | Delist URL |
|---|---|---|---|
| Spamhaus ZEN | IP | 🔴 Critical | spamhaus.org/delist |
| Spamhaus DBL | Domain | 🔴 Critical | spamhaus.org/delist |
| Barracuda | IP | 🟠 High | barracudacentral.org/rbl/removal-request |
| SORBS | IP | 🟠 High | sorbs.net |
| SpamCop | IP | 🟡 Medium | spamcop.net/bl |
| UCEPROTECT | IP | 🟡 Medium | uceprotect.net/en |
| PSBL | IP | 🟡 Medium | psbl.org |
| URIBL | Domain | 🟡 Medium | uribl.com |
The #1 reason legitimate senders get blacklisted is poor email authentication DNS records. Missing or broken SPF, DKIM, and DMARC records signal to receivers that your domain might be used for spoofing. Receivers may then report your mail as spam, triggering blacklists.
If more than 0.1% of recipients mark your email as spam (the "complaint rate"), inbox providers flag your domain. Google Postmaster Tools tracks this — a complaint rate above 0.3% gets you into deliverability trouble.
High bounce rates from non-existent addresses (hard bounces) signal poor list hygiene. Blacklists like SORBS specifically track addresses that generate bounces.
If you use a shared hosting provider or email service, another user's bad behavior can get the IP blacklisted — affecting your mail too. Always check your sending IP before signing up for an ESP.
Sending significantly more email than usual (e.g., a sudden campaign to 50,000 recipients) can trigger spam filters. Warm up your IP gradually: start at 100/day and increase 20-30% daily.
Before requesting delisting, fix whatever caused the listing:
Most blacklists have an automated delisting process:
spamhaus.org/delist — usually processes within 24 hours after you've fixed the issue. Read their block listing carefully.barracudacentral.org/rbl/removal-requestsorbs.net — may require waiting 48 hours after fixingAfter delisting, implement these safeguards:
| Factor | Blacklist | DNS Deliverability |
|---|---|---|
| What it is | Your IP/domain is in a spam database | Your DNS records aren't configured for email auth |
| How to check | Query DNSBLs | Check SPF/DKIM/DMARC records |
| Impact | Mail rejected/filtered by receivers | Mail flagged as suspicious, no authentication pass |
| How to fix | Delist request + stop spam behavior | Fix DNS records (SPF, DKIM, DMARC) |
| Prevention | List hygiene, low complaint rate | Correct DNS configuration |
| Relationship | Poor DNS config → more spam reports → blacklisting | |
The key insight: DNS misconfiguration is the #1 preventable cause of blacklisting. When your SPF, DKIM, or DMARC records are broken or missing, receivers can't verify your email, leading to spam folder placement. Users then report it as spam, which triggers blacklisting. It's a cascade — and fixing DNS stops it at the source.
Use this checklist to keep your domain off blacklists and maximize inbox placement:
Our free API makes it easy to monitor your domain's deliverability configuration programmatically:
# Check a single domain
curl https://korpo.pro/api/v1/check/yourdomain.com
# Batch check multiple domains
curl -X POST https://korpo.pro/api/v1/batch \
-H "Content-Type: application/json" \
-d '{"domains":["sendgrid.com","mailchimp.com","postmarkapp.com"]}'
The response includes a 0-100 deliverability score broken down by protocol, plus specific issues and recommendations. Set up a cron job to check weekly and alert when your score drops.
Most auto-delisting processes take 24-48 hours after you've fixed the root cause. Spamhaus PBL and SpamCop auto-expire listings. Manual delisting requests (Spamhaus SBL, Barracuda) can take 1-7 business days.
Yes — services like MXToolBox and MultiRBL.valli.org check 100+ blacklists simultaneously. For ongoing monitoring, you can also script DNSBL queries using our API to check the DNS configuration that causes blacklisting.
Major ESPs have dedicated deliverability teams and get delisted quickly. If your ESP's shared IP is listed, contact their support. Long-term, consider a dedicated IP ($20-50/month from most ESPs) so other senders can't affect your reputation.
Yes. IP blacklists (like SORBS, Spamhaus SBL) block specific sending IPs. Domain blacklists (like Spamhaus DBL, URIBL) block domains regardless of which IP sends from them. You can be listed on one, both, or neither. Domain listings are harder to escape because switching IPs doesn't help — you have to delist the domain itself.
Gmail uses a combination of DNSBLs (including their own), machine learning-based spam filters, and sender reputation signals. Being listed on Spamhaus will definitely affect Gmail delivery, but even without blacklist listings, poor DNS authentication (SPF/DKIM/DMARC) hurts Gmail inbox placement.
Free instant audit of SPF, DKIM, DMARC, MTA-STS, TLS-RPT, and BIMI — the DNS records that prevent blacklisting.
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