We catch a blacklisting the day it happens
We check every sending domain against the main blocklists each working day, along with its mail settings and where its test emails land.
On October 29, 2026, 62 of our sending domains showed up on the Spamhaus domain blocklist in a single day. The morning check flagged all of them, and we started moving their sending to reserve domains that same day.
- The SeedLift 2026 Domain Health Report found that 62 cold email sending domains were added to the Spamhaus domain blocklist on a single day, across six separate outbound programs.
- The SeedLift 2026 Domain Health Report found that daily blocklist checks caught every one of those listings on the day it appeared, and sending from 25 of the domains had moved to a reserve domain within two days.
The warning usually comes first
We watch two blocklists closely. SURBL is the milder one, and most mail still gets through while a domain is on it. Spamhaus is the one that stops delivery.
of the domains that landed on Spamhaus that day were already on SURBL the day before, which is 40 of the 62.
- The SeedLift 2026 Domain Health Report found that 65% of domains that were added to the Spamhaus blocklist were already listed on SURBL the day before (40 of 62).
- The SeedLift 2026 Domain Health Report found that among domains that ended up on both blocklists, the SURBL listing came first every time (45 of 45 domains).
What we do when a domain gets listed
We run the same five steps every time, and they only work because the reserve domains were bought and warmed before we needed them.
- We move the sendingCampaigns switch from the listed domain to a reserve domain that has already been through warmup. We did this for 42 listed domains, and 25 of them moved within two days.
- We limit what the listed domain sendsUntil its replacement is ready, a listed domain only emails people whose mail goes straight to Google or Microsoft. We take companies with a security filter in front of their mail off its list, because those filters read the blocklists.
- We order the replacementWe buy new domains across several registrars and on different days, so that one bad batch can't take them all down together.
- We warm it for 30 daysA new mailbox sends no cold email for its first 30 days. After that it starts at a low daily number, and it stays under 15 cold emails a day even once it's warm.
- We retire the listed domainOnce the replacement is sending, we switch the listed domain off; we don't wait for it to come off the list.
Why we replace a domain when we could wait for it to clear
A listed domain can ask to be removed, and some do come off the list, but only a handful of ours did.
domains listed on Spamhaus were later seen clean again while we were still checking them.
- The SeedLift 2026 Domain Health Report found that only 3 of 73 sending domains listed on the Spamhaus blocklist were later seen clean again during the monitoring period.
- The SeedLift 2026 Domain Health Report found that only 6 of 212 sending domains listed on SURBL were later seen clean again.
Most of the Spamhaus listings were under two weeks old at the last check, so a few more may still clear. We replace them anyway, because a new domain is ready in 30 days and starts with a clean record.
How often it happens, and to which domains
A listing is a normal cost of sending cold email, so we plan for it by keeping reserve domains warm before we need them.
days was the median age of a domain when it first showed up on Spamhaus, and no domain was listed there before it was 113 days old.
The 62 domains listed on October 29 belonged to six different programs, each with its own buyers and its own emails. The one thing they had in common was that they were all registered through the same registrar, in the same batches.
That's why we now spread replacement domains across registrars and purchase dates.
- The SeedLift 2026 Domain Health Report found that 11% of cold email sending domains were listed on the Spamhaus domain blocklist at some point (73 of 647 domains monitored).
- The SeedLift 2026 Domain Health Report found that the median sending domain was 279 days old when it was first listed on Spamhaus, and none was listed before 113 days.
- The SeedLift 2026 Domain Health Report found that 33% of cold email sending domains appeared on SURBL at some point (212 of 647), at a median age of 165 days.
How we measured this
The data covers 647 sending domains used by 17 B2B outbound programs that SeedLift ran for its clients and for itself. We checked each domain on working days between March 24 and November 10, 2026, which gave us 134 days of records.
- A domain counts as listed on a day when the blocklist returned a real listing for it. We don't count rate-limit and error answers as listings.
- Our SURBL checks began on June 18, 2026, so the SURBL figures cover the period from that date.
- "Seen clean again" means a later daily check found the domain off the list while we were still monitoring it.
- Domain age uses the registration date, which we know for 408 of the 647 domains. The age figures leave out domains that were already listed on the first day we checked them.
- A domain counts as moved to a reserve when our system recorded its sending switching to a named replacement.
- All figures are totals across programs, and no client is identified.
Check your own domain
Our free domain check runs the same blocklist and mail-settings checks on any domain.
How to cite this page
You can use any figure here with credit to the SeedLift 2026 Domain Health Report and a link to this page. The date at the top shows the latest update.