What DNSBL blacklists such as Spamhaus, Barracuda and SpamCop are, how to check whether your IP address is listed, why it got there and how to get it removed.
Blacklists (DNSBLs, also called RBLs) are databases of addresses that have sent spam or launched attacks. Mail servers check them before accepting a message: if the sender’s address is listed, the message is rejected or put in the spam folder. A rejection usually looks like this:
550 5.7.1 Service unavailable; client [203.0.113.10] blocked using zen.spamhaus.orgHow to check
To check dozens of lists at once, use MXToolbox or multirbl.valli.org. Check the most influential list, Spamhaus, on its own website: check.spamhaus.org.
To check by hand, make a DNS query. Write the address backwards and follow it with the list’s zone. For 203.0.113.10:
dig +short 10.113.0.203.zen.spamhaus.orgAn empty answer means the address is not listed. An answer such as 127.0.0.2 means it is listed; the last number shows which Spamhaus list it is on.
127.255.255.254 — this is a refusal, not a listing. Through 8.8.8.8 it is worse: you get an empty answer, as if the address were not listed. Check from a server with its own DNS resolver, or on the Spamhaus website.Why an address gets listed
- A mailbox has been hacked and is being used to send spam. Change the password and scan your computer with antivirus software.
- A website has been hacked and a script on it is sending email: Site hacked: what to do.
- The server is infected, or the mail server is relaying other people’s mail (an open relay).
- A mailing to people who did not agree to receive it — recipients click “This is spam”.
- The address used to belong to someone else and was already listed — this happens with new servers.
Fix the cause first. If you get the address removed from a list and the mailing carries on, it will be listed again — and getting off the list a second time is harder.
How to get off a list
| List | What to do |
|---|---|
| Spamhaus SBL, XBL, CSS | once the cause is fixed, submit a removal request at check.spamhaus.org |
| Spamhaus PBL | addresses that are not expected to send mail directly; if you run a mail server with a correct PTR record, submit a removal request at the same place |
| Barracuda | removal form |
| SpamCop | the address is removed automatically once the complaints stop |
| UCEPROTECT levels 2 and 3 | these block whole provider networks; the listing disappears by itself once spam stops coming from the network; there is no need to pay for faster removal |
Removal usually takes from a few hours to a day. After that, check the address again.
If the address is ours
- Hosting. If mail from your domain is rejected because of a blacklist, contact our support team: this is the address of our server, and we deal with it.
- Cloud server. You send the mail from it, so you are the one to fix the cause. If a list needs a request from the network owner, get in touch with us and we will confirm it.
To keep your mail out of spam even without blacklists, check your domain’s settings: Email going to spam: why and what to check.
Didn’t find the answer? Ask our support team — we’ll help.