Things to know about Blacklists - Online Help | Zoho Campaigns

Things to know about Blocklists

In short: a blocklist (formerly "blacklist") flags IPs and domains suspected of sending spam, and providers use it to filter or reject their mail. If you land on one, stop sending, find which list flagged you, fix the underlying cause (usually list hygiene, complaints, or spam traps), then request delisting. The best defense is clean, permission-based, authenticated sending.
A blocklist is a list of IP addresses and domains suspected of sending spam. Services such as Spamhaus, Barracuda, and SpamCop maintain their own lists, and ISPs and mailbox providers use them to block or filter suspected senders. (These are increasingly called "blocklists" rather than "blacklists," and many providers now weigh reputation signals such as complaint rate and engagement alongside blocklist status.)

Blocklists – An infographic.

What to do if your domain is blocklisted

If your IP or sender domain is on a blocklist, act right away:
  1. Use a blocklist lookup tool to find exactly which services have listed you.
  2. Identify and fix the root cause before anything else — most listings won’t clear (or will re-list) until the underlying problem is resolved.
  3. Submit the delisting request form the service provides. Note that some lists (such as Spamhaus) require you to fix the cause first, and some minor listings expire on their own once the bad behavior stops.
  4. Analyze why it happened and take prompt action to prevent a repeat.
Avoid sending until you’re delisted — continuing to send can make things worse and get you listed by additional services.
You can check your status with lookup services such as MXToolbox, DNSBL.info, MultiRBL, BlacklistAlert.org, Spamhaus, and Barracuda Central. It also helps to monitor your reputation continuously in Google Postmaster Tools and Microsoft SNDS, which surface problems before they escalate to a listing.

How a blocklisted domain affects your messages

  • Poor delivery — emails are rejected or pushed to spam/junk.
  • A worse reputation with other blocklist and anti-spam services.
  • A high bounce rate from recipient systems.
The main things that get a sender domain or IP blocklisted are poor list management and poor sending practices, covered below.

Poor list management

A mailing list that isn’t maintained is the single biggest cause of blocklisting. Three specific problems stand out.

Abuse complaints

Complaints are a major cause. When recipients mark your email as spam, filters at every level treat you as suspicious, and a high complaint rate can get you listed. This now has a hard line attached: Google and Yahoo require bulk senders to keep their spam-complaint rate below 0.3% (aim for under 0.1%). Recipients can also report you directly to anti-spam services or to Zoho Campaigns, since your mail was sent through us — and direct abuse complaints escalate blocklisting fastest. Learn how to tackle complaints.

Spam traps

Blocklist services use spam-trap addresses to catch senders with poor list hygiene. Traps look like normal addresses but never opt in or respond, and they’re much harder to spot than bounces or complaints. Remove or suppress addresses that have never engaged, especially long-dormant ones — abandoned addresses are sometimes recycled into traps (often roughly a year after they go inactive). Base "dormant" on clicks and conversions rather than opens, because Apple’s Mail Privacy Protection now inflates open data and can make dead addresses look active.

High unsubscribes

Unsubscribes are normal, but a sharp or sustained spike is read as a negative signal that degrades your domain reputation and, if severe enough, can contribute to a listing. Treat a rising rate as a warning to adjust your content, targeting, or frequency.

Poor email sending practices

These practices damage your sender reputation and can lead to a listing.

Sender recognition failure

People open email only when they trust the sender; otherwise they ignore, delete, or report it. Those negative responses degrade your reputation and can lead to blocklisting. Authenticate your mail (SPF, DKIM, DMARC — required for bulk senders since February 2024) and keep a consistent identity so recipients recognize you. Learn more about sender recognition.

Improper contact engagement

People forget. Email someone after a long silence and they may not recall subscribing, which leads to complaints. Keep a steady, predictable cadence. Send regularly to engaged contacts, segment those who’ve gone quiet, win them back with re-engagement campaigns, and remove the ones who stay unresponsive. Learn more about list segmentation. (Judge "quiet" by clicks and conversions, not opens, since open data is no longer reliable.)
A link to a blocklisted domain harms your email and your own domain. Avoid public URL shorteners — they’re abused by spammers and can drag you down; prefer links on your own domain or a branded tracking domain. Before you send, make sure none of your links point to listed domains.

Irrelevant or deceptive content

If your subject line doesn’t match the email’s content, recipients feel deceived and report it as spam — which can lead to a listing (and violates anti-spam rules against deceptive subjects). Keep your subject line, message, and any linked landing pages consistent with each other.

Sending from a new domain

  • If the new domain differs from the one contacts signed up on, tell them it’s you: add a footer line like "You’re receiving this because you subscribed at yourdomain.com."
  • A new domain has no track record, so providers are cautious and may defer your mail. Authenticate it, then warm up gradually — segment your list and increase volume step by step as your reputation builds.

How to avoid getting blocklisted

  • Monitor your reputation regularly with active services such as Spamhaus, SpamCop, and Barracuda, plus Google Postmaster Tools and Microsoft SNDS.
  • Watch your bounce rate and read the error messages. If a bounce says you’re listed on a blocklist, submit a delisting request to that service once you’ve fixed the cause.
  • Send only to permission-based, engaged contacts; authenticate; and keep complaints under 0.1%. Prevention is far easier than delisting.