Email Blocklists: How to Check If You're Listed and Get Removed

Your Tuesday campaign went out to the same list as always, and by Wednesday morning your open rate had fallen from 34% to 4%. Nothing about the email changed. The bounce log is full of SMTP 550 rejections with a URL in the error text. That URL points at a blocklist, and until you deal with it, every send you make is being thrown away before anyone sees it.

Blocklists are the least discussed part of deliverability because most senders never touch one. When you do, the failure is total rather than gradual. You are not landing in spam, you are being refused at the door. The recovery is procedural and usually fast, but only if you fix the cause first. Delisting a domain whose underlying problem is still live gets you relisted within days, and repeat listings make the next removal slower.

Before you start

You need three things in front of you.

A bounce log with full SMTP responses. Not the summary count in your dashboard, the actual rejection strings. Every real blocklist rejection names the list and usually includes a lookup URL. Without this you are guessing at which list you are on, and there are hundreds of them.

Your sending IP address and your sending domain. These are two separate reputations and they land on separate lists. If you send through a shared pool at MailerLite or Brevo, the IP is not yours and you cannot delist it: the ESP has to. Your domain is always yours.

DNS access, or someone who has it. Some removals require you to prove control of the domain, and every real fix involves checking authentication records.

Step 1: Find out which list you are actually on

Run your IP and your domain through Spamhaus’s own lookup tool first. Spamhaus is the list that matters most. It is referenced by corporate mail filters worldwide, and a listing there stops delivery broadly rather than at one provider. Spamhaus maintains several lists and the distinction decides how you get off:

• SBL: a human at Spamhaus decided to list you. Removal goes through human review.
• CSS: an automated listing, usually triggered by snowshoe patterns or sending from an IP range with a bad neighbourhood. Self-service removal.
• XBL: your machine looks compromised or is relaying. Fix the compromise or removal is pointless.
• PBL: the IP is in a range its owner says should not send mail directly. This one is usually your hosting provider’s job, not yours.
• DBL: your domain is listed, not your IP. Changing IPs does not help you here.

Then check Barracuda’s Reputation Block List. Barracuda matters because a large share of businesses run Barracuda appliances in front of their mail, so a listing there is felt almost entirely in B2B sending: your consumer campaigns look fine while your sales pipeline goes silent.

Everything else is a lower priority. SpamCop listings expire on their own roughly a day after the last spam report, so the fix is to stop the cause and wait. UCEPROTECT’s higher tiers list entire network ranges based on the behaviour of unrelated neighbours, and most receiving providers treat them as informational rather than blocking. Do not spend a Saturday chasing a UCEPROTECT Level 3 listing while a Spamhaus SBL entry sits unaddressed.

Step 2: Find the cause before you request anything

Listings are symptoms. Work through the plausible causes in order of how common they are.

You mailed a list you should not have. An imported list from an acquisition, a re-engagement send to addresses untouched for three years, a purchased file someone in sales swore was opt-in. Old addresses decay into spam traps, and hitting traps is the fastest route onto Spamhaus. Our list cleaning guide covers how to identify the risky segments before you send to them.

Something of yours is compromised. A hacked CMS, a leaked SMTP credential, a contact form with no rate limit. If your volume graph shows sends you cannot account for, stop looking at your marketing program and start looking at your server.

Your complaint rate crossed a threshold. Gmail, Yahoo and Microsoft want bulk senders under 0.30% spam complaints. Sustained complaints above that feed the reputation signals blocklists watch.

Your authentication broke. An SPF record that stopped covering a new sending service, a DKIM key rotated on one side only. Misaligned mail from your domain looks like spoofed mail from your domain. The SPF, DKIM and DMARC guide covers the records and how to read them.

You did nothing at all. Shared IP pools mean you inherit your neighbours’ behaviour. If the IP is not yours, this is your ESP’s problem to solve. Open a ticket with the sending IP and the exact rejection text and let their deliverability team handle the removal.

Step 3: Fix it, then request removal

Suppress the segment that triggered it. Rotate the leaked credential. Repair the DNS record. Then submit the removal request through the correct form for your specific list: Spamhaus routes SBL and CSS listings differently, and using the wrong one adds days.

Write the request like an incident report, not an apology. State what happened, what you changed, and what prevents a repeat. “We imported a 2019 event list without re-permissioning it, we have suppressed all 14,000 addresses from that import, and imports now require a double opt-in confirmation” gets processed. “Please remove us, we are a legitimate business” does not.

Legitimate SBL and XBL removals typically clear in 24 to 72 hours. Automated CSS removals are faster. Barracuda’s form is self-service and usually resolves within a day, though they will re-list you immediately if the traffic pattern continues.

Step 4: Set up monitoring so the next one is not a surprise

The gap between being listed and noticing is where the damage happens. Most senders find out from a collapsed open rate several days later, by which time they have burned a campaign and part of their domain reputation.

Automated blocklist checks close that gap. MailerSend added blocklist monitoring to its platform in March 2026. It checks your domains and IPs on a schedule, alerts an email address or webhook when something appears, and scores each list by how much it actually affects delivery so you can tell a Spamhaus hit from noise. It is a transactional email service, so it will not run your marketing campaigns, and the monitoring covers a curated set of lists rather than every list in existence.

If you would rather not add another vendor, a standalone monitoring service or a weekly calendar reminder to run the two lookups above will catch most of what matters. The mechanism is less important than the fact that something checks when you are not looking.

Which platforms make this less painful

The platform you send through decides how much of this you can see and how much you have to do yourself.

Postmark gives the clearest view of what is happening to individual messages. Its bounce records carry the full SMTP response rather than a summarised category, which is exactly what you need in step 1, and it publishes its own delivery time data openly. Its free Developer plan covers 100 emails a month and Basic starts at $15 a month for 10,000 emails. The catch is scope: Postmark bans cold outreach and enforces tight content rules to keep its shared pools clean, and it is not a marketing platform, so you will run something else alongside it. Its DMARC monitoring is also a $14/month add-on rather than an included feature.

Mailgun gives you more raw control: dedicated IPs, detailed logs, and per-domain separation so a problem in one sending stream does not contaminate another. The free tier allows 100 emails a day and Basic starts at $15 a month for 10,000 emails. The weak spot is that the data you need during an incident sits behind the upper tiers: Basic keeps only short log retention, overages run $1.80 per 1,000 messages, and additional dedicated IPs are $59 each per month. Working out a listing on the entry plan often means the logs have already rolled off.

For marketing rather than transactional mail, MailerLite handles the IP side for you. You send from its shared pools, which means its deliverability team monitors and delists on your behalf, a genuine advantage for a small team with no one on call for this. It verifies your SPF and DKIM records and reports problems in plain language. The free plan covers 250 subscribers and 2,500 emails a month, and the Comfort plan starts at $12 a month for 500 subscribers. The trade-off is the flip side of the same arrangement: you have no visibility into or control over the IP reputation you depend on, and its automation is thinner than what ActiveCampaign offers. Support is chat and email only, with no phone line for the afternoon your sending stops.

Where people go wrong

• Requesting removal before fixing the cause. The single most common mistake, and it makes every subsequent request slower.
• Chasing every list they appear on. Hundreds of blocklists exist and most have no measurable effect on delivery. Spamhaus and Barracuda first; treat the rest as diagnostic signal rather than work items.
• Assuming a new IP solves it. If the listing is a Spamhaus DBL entry against your domain, or your problem is a bad list, a fresh IP just moves the same behaviour somewhere new.
• Blaming the ESP for a domain listing. Your ESP owns the IP reputation on shared pools. Your domain reputation is yours regardless of who sends for you.
• Treating it as a one-off. A listing means your sending practice produced conditions a blocklist objected to. Nothing about that changes when the entry is removed.

What success looks like

You are done when three things are true. Both lookups return clean for your domain and your sending IP. Your bounce log for a small test send shows normal delivery with no 550 rejections referencing a list. And something automated is watching, so the next listing reaches you as an alert rather than as a bad week of metrics.

Then go back to the cause. Almost every blocklist incident traces to list quality or authentication, and both are cheaper to maintain than to repair. The deliverability guide covers the reputation work that keeps you off these lists, and the deliverability-focused platform roundup ranks tools on inbox placement rather than feature count.

Pricing verified 3 August 2026 against our pricing audit: Postmark, Mailgun and MailerLite entry tiers and add-ons. Vendor prices change. Confirm on the provider’s own pricing page before you budget.

Sources

1. Spamhaus — IP and domain reputation lookup — accessed 2026-08-03
2. Barracuda Central — Reputation Block List removal request — accessed 2026-08-03
3. MailerSend — Blocklist monitoring — accessed 2026-08-03