One listing on a DNS blacklist and your invoices, password resets and newsletters end up in spam or bounce outright. m0nitor checks your IP addresses against the common blacklists and alerts you when a listing appears.
The lists that matter: Spamhaus ZEN, SpamCop and Barracuda by default, plus SORBS, UCEPROTECT, PSBL and Mailspike if you want them.
Single IPs or networks: Watch one address or an IPv4 network of up to 256 addresses, such as the /24 of your mail cluster.
Your own threshold: Decide how many listings make the monitor go down, so one aggressive list does not wake anyone.
Alerts and history: Listings open an incident and run your workflows; the history shows when an address was listed and delisted.
Why blacklist listings hurt
Mail providers check the sending IP against DNS blacklists (DNSBLs) before they accept a message. A listing on Spamhaus alone is enough for many of them to reject or junk your mail, often without the sender noticing.
Listings happen for reasons outside your control too: a compromised account sending spam, a neighbour in a shared range or a misconfigured relay. The sooner you know, the sooner you can fix the cause and request delisting.
How m0nitor checks
Each address is looked up in the zone of every selected blacklist
An answer in 127.0.0.0/8 counts as listed, as defined by the DNSBL convention
IPv6 addresses are checked against the lists that support IPv6, such as Spamhaus ZEN
Results stay visible per list, so you know where to request delisting
Set up in three steps
Add a blacklist monitor: Enter an IP address or an IPv4 network in CIDR notation.
Choose the lists: Keep the default lists or add more, and set how many listings count as down.
Route the alert: Send listings to email, Slack, Teams or wherever your mail admins work.
Plan availability
Blacklist monitoring is part of the Business and Enterprise plans.
Spamhaus ZEN, SpamCop and Barracuda by default. You can add SORBS, UCEPROTECT Level 1, PSBL and Mailspike per monitor.
Can I monitor a whole network?
Yes, an IPv4 network of up to 256 addresses, for example a /24. Each address in the range is checked against the selected lists.
Does m0nitor remove my IP from a blacklist?
No. Delisting is requested at the blacklist operator after the cause is fixed. m0nitor tells you which list lists which address, so you know where to go.
Is blacklist monitoring the same as an SPF or DMARC check?
No. SPF, DKIM and DMARC are DNS records you publish; a blacklist is a third-party verdict on your IP. Both affect delivery, and you can check the records with the free DNS lookup.