Email Deliverability
Mail Server Blacklisted
When a mail server's IP address or sending domain appears on email blacklists (RBL/DNSBL), receiving servers reject or flag messages from it. Blacklisting can affect your entire domain's email deliverability and is often caused by spam originating from the server, compromised accounts, or inheriting a blacklisted IP from a previous user.
Symptoms
- Email bounces referencing specific blacklist names
- Rejection messages containing "550 5.7.1" or blacklist URLs
- Sudden drop in email deliverability across multiple recipients
- Delivery delays with messages stuck in the outbound queue
Common Causes
- Compromised email account sending spam
- Open relay allowing unauthorized message sending
- Sending to purchased or scraped email lists
- Shared IP inherited from a previous spammer
- Virus-infected server sending malicious emails
Step-by-Step Troubleshooting
- 1
Check domain blacklist status
Scan your domain against major blacklist databases.
Use Domain Blacklist Check → - 2
Check IP blacklist status
Scan your mail server IP against RBL/DNSBL databases.
Use IP Blacklist Check → - 3
- 4
Secure the server
Close open relays, patch vulnerabilities, and change compromised credentials.
- 5
Request delisting
Submit delisting requests to each blacklist provider after resolving the root cause.
Recommended Diagnostic Tools
Monitor Blacklist Status
Get instant alerts if your mail server appears on any blacklist.