Question 1

What is a DNSBL/RBL blocklist?

Accepted Answer

A DNSBL (DNS-based Blackhole List) or RBL (Real-time Blackhole List) is a list of IP addresses or domains known to send spam. Mail servers check these lists to decide whether to accept, reject, or flag incoming emails.

Question 2

How do I get delisted from a blocklist?

Accepted Answer

Each blocklist has its own delisting process. Most provide a self-service form on their website. First, fix the underlying issue (compromised server, spam complaints, open relay), then request removal. Some lists auto-delist after a period of no spam activity.

Question 3

Which blocklists matter the most?

Accepted Answer

Spamhaus (ZEN, DBL) is the most impactful - used by most major mailbox providers. Barracuda (BRBL), SpamCop, and SORBS are also widely used. Being listed on any of these will significantly affect your deliverability.

Question 4

Can I check both IP and domain blocklists?

Accepted Answer

Yes. IP blocklists (DNSBL) check your sending server's IP address. Domain blocklists (URIBL, SURBL, DBL) check your domain name. Both types affect email deliverability. This tool checks the appropriate list type based on your input.

Question 5

Why is my IP blocklisted?

Accepted Answer

Common reasons include: sending spam (intentionally or from a compromised server), high bounce rates or spam complaint rates, open relay configuration, shared IP with a spammer, or being part of a botnet. Check your server security and sending practices.