Short version: neither a SURBL listing nor a Spamhaus DBL listing has any practical impact on your deliverability to business mailboxes in 2026. If your domains show up on either list, there is no need to panic, pause campaigns, or make major changes — keep warming up and keep sending. We know this contradicts a lot of what is written online; it is what we see in our own tests, every time. Details on Spamhaus DBL are below.
Why a SURBL listing is not a problem
Google has effectively stopped paying attention to SURBL, largely because it began flagging far too aggressively over the past year — to the point of affecting paid Google/Microsoft enterprise infrastructure and legitimate businesses. Google was the last of the major ESPs still consuming SURBL, and it stopped doing so within the last year. A couple of small providers may still consume SURBL-family lists, but their combined market share is small enough that it isn't worth planning around.
A real example from our own accounts: one client had 188 domains listed on SURBL and kept sending cold email throughout. Their reply rate did not change at all, and we continued to see solid spam-test results from those same listed domains.
A few important technical points:
SURBL lists the domain (URL reputation), not your sending IP.
Our sending IPs are not blacklisted — they stay green, and we rotate IPs automatically.
A SURBL "multi" listing in tools like MXToolbox or an Instantly warning ("contains a URL listed in the ABUSE SURBL blocklist") doesn't reflect inbox placement and doesn't need action. The same applies to similar link/URL-reputation lists such as SpamRATS.
We don't file SURBL delisting requests on your behalf, because the listing has no delivery effect; a listed domain is fully usable with Maildoso mailboxes.
Our own infrastructure domains show up on SURBL too — that's expected
If you run a full DNS/SPF audit, you may notice that the relay domains we include in your SPF record (the ones behind our sending infrastructure) are themselves SURBL-listed, not just your own domains. This is expected and not a sign of a platform-wide outage or a defect in your specific account. Because the sending pool is shared and centrally managed, we can't move an account to a different relay pool.
Here's why it doesn't translate into a deliverability problem for you:
SURBL scores the domain shown in a URL inside a message body, not the server or IP that relayed the message. Our infrastructure domains being listed doesn't change how Google or Microsoft treat the IP your mail actually sends from.
We operate sending infrastructure at very high volume (80M+ emails/day), which is exactly the kind of footprint that tends to accumulate SURBL "abuse" listings over time even when actual inbox placement is healthy — the two are measuring different things.
Mailbox providers made the shift away from weighting SURBL industry-wide starting in late 2025. AI-based audit tools trained on older data still flag SURBL as high severity, so you'll keep seeing it surfaced as "critical" in automated reports regardless of real-world impact.
If you're seeing this in a third-party or AI-generated audit alongside other findings (DKIM, DMARC, redirect checks), it's worth having us review the specific finding rather than treating the whole report as evidence of an infrastructure problem — some of those checks don't apply cleanly to how our managed DNS and our own DKIM signing are set up.
"But my audience sits behind security gateways, or uses SpamAssassin"
This comes up most often from senders whose recipients are technical buyers — MSPs, IT and security teams — who run email security stacks in front of their mailboxes. The concern is reasonable, but it doesn't change the conclusion above.
A SURBL flag doesn't automatically mean SURBL is what filtered you. Every major provider inspects the links and content of a message anyway — a plain Google Workspace inbox runs its own link and content checks with no SURBL involved. So seeing a URL-reputation listing does not by itself identify the cause of a placement problem.
SpamAssassin is not a meaningful factor for B2B lists. We don't see SpamAssassin actively used on corporate mailboxes — it shows up mostly on self-hosted and open-source mail stacks. For a typical B2B recipient list, it's likely that effectively none of your leads are scored by it, which also means a SpamAssassin seed result is not representative of where your mail actually lands.
You can size your own exposure directly. Check the MX records of your lead list to see what share of your recipients resolve to Google or Microsoft versus a security gateway (Barracuda, Proofpoint, Mimecast, and similar). That MX breakdown is the honest measure of how much filtering-gateway exposure your audience really has — far more useful than reasoning from a blocklist flag.
What you should do
Keep warming up your mailboxes at the recommended volume (see What's the daily email limit per email account?).
Keep your campaigns running — there's no need to pause, reduce sending volume, or otherwise change your strategy because of a SURBL listing.
Do not delete mailboxes or domains in reaction to a SURBL listing, and there's no need to purchase new domains — SURBL-listed domains are still fully usable with Maildoso mailboxes.
Not the same as a registrar suspension
A SURBL listing is very different from a registrar/registry suspension, which is a hard block that stops a domain from resolving or sending until it is reinstated. If a domain is actually suspended (rather than just SURBL-listed), contact support to confirm the status and discuss options such as a replacement domain.
If a domain is experiencing confirmed performance issues that meet Maildoso's eligibility criteria, up to four replacement domains may be provided within one year of domain purchase. However, a SURBL listing alone does not qualify as a performance issue under this policy. Additionally, Maildoso does not consider a SURBL listing as a valid reason for free mailbox replacements, billing credits, or refunds. This policy ensures clarity for users regarding the implications of SURBL listings and aligns with Maildoso's approach to email deliverability management.
What about Spamhaus DBL?
Spamhaus DBL is also a domain list (not an IP list) and is a different signal from SURBL — but the conclusion is the same: a Spamhaus DBL listing does not affect your deliverability to business mailboxes, Google Workspace or Microsoft 365. We know that contradicts a lot of what's written online. We have run multiple tests on DBL-listed domains, and every time a domain is properly warmed up it shows 10/10 inbox placement — the same as unlisted domains. Google stopped using Spamhaus DBL as a spam signal in August 2026, and none of the major mailbox providers consume it today.
Spamhaus has become noticeably more active in 2026. It now lists batches of lookalike or branded domains bought at the same time — often within a day, sometimes before a single email has been sent. That is a pattern-based listing driven by domain names, not a verdict on anything you did and nothing to do with Maildoso's infrastructure. Customers who buy generic domains with no shared keywords usually don't get listed at all.
What to do about a DBL listing:
Nothing dramatic. Keep warmup at the recommended 80/day with a 45% reply rate and keep your campaigns running. A properly warmed domain delivers normally whether or not it is listed, so the listing itself needs no reaction.
If the listed domain is new and still warming up, simply finish the standard warmup period before you start campaigns, as you would anyway. Being a little more conservative with a brand-new listed domain — an extra few days of warmup-only before cold sending — does no harm, but it is optional.
Don't delete or replace the domain in reaction to the listing, and don't file a delisting request. Spamhaus's published position is that cold outreach is spam, so it generally won't delist a domain used for it regardless of what you fix — and since the listing isn't affecting your delivery, there's nothing to recover.
A DBL listing on its own never qualifies for a free replacement domain, free mailboxes, a credit, or a refund.
How to get listed less often. Spamhaus specifically looks for batches of lookalike domains pointing to the same brand (yourbrand-hq.com, getyourbrand.com, tryyourbrand.com, and so on). Choosing unique, generic domain names instead — names that don't share a root with each other or with your main site — drastically reduces how often new domains get listed. See What are the best practices for configuring domains?
If you're looking at a Spamhaus CSS/SBL/XBL entry for an IP rather than a domain, that's about our rotating sending pool, not your domains. Some of our IPs will always be on one list or another — that's the nature of cold-email infrastructure — and we rotate listed IPs out automatically, so it doesn't affect what you send. See One of my sending IPs shows as blacklisted.
My domain is listed before I've even sent an email yet
It's normal to see a brand-new domain flagged on SURBL, Spamhaus DBL, or a similar list like SpamRATS before you've sent a single campaign email — these lists often pick up domains from bulk registration/DNS patterns, not from anything you've sent. The guidance above applies the same way: this isn't a signal your domain is untrustworthy, and there's nothing to fix before you start warming up.
Seeing an IP flagged instead of a domain?
Everything above is about SURBL/URL-reputation lists, which flag domains, not IPs. If what you're actually looking at is a sending IP address showing as blacklisted, or a mailbox labeled "burned" or low-reputation, that's a different situation with its own guidance — see One of my sending IPs shows as blacklisted and My mailboxes show as "burned", "blacklisted", or low reputation — what it means.
Seeing real placement problems, or other deliverability questions?
If your emails are actually landing in spam or being rejected — not just listed — that deserves a proper look regardless of any blocklist. The fastest route is a free Deliverability Audit with one of our specialists: log in, click the Deliverability Audit button in the top-right of your dashboard, and pick a time. Our expert will review your warmup, sending settings, domains and placement results with you on a call. You can also send us your account email, the affected domains or mailboxes, one full message header or your latest placement-test result, and your current warmup settings; the most common real cause we find is warmup volume that's too low or too new. If a blacklist flag is the reason you're considering a refund, see Domains flagged as blacklisted: how we help, and where refunds fit in.
Maildoso also offers an 80% inbox-placement commitment as part of its Terms of Service, subject to proper warmup and sending practices. In cases of qualifying domain performance issues, users may be eligible for up to four replacement domains within one year of domain purchase. However, a SURBL or Spamhaus DBL listing alone does not qualify for billing credits, refunds, or domain or mailbox replacements, as neither is treated as a cause of deliverability issues.