Catch-all Domains in B2B Lists, 2026: 30.8% of Business Domains Accept Every Address
About one business domain in three will not tell you whether a mailbox exists. Between 11 and 25 October 2026, 4,994 of the 16,199 business domains that gave SimpleVerifier's SMTP check a definite answer (30.8%) accepted a made-up address as readily as a real one. That is what "catch-all" or "accept-all" means: every address looks deliverable at check time, so a real person and a typo get the same answer.
The second finding is about how B2B lists get built. When an address was one of three or more spellings of the same name on a domain (first.last, flast, firstl and so on, the output of an email permutator or finder), it existed 1.6% of the time. An address checked in one spelling existed 37.4% of the time.
Catch-all domains by mail host
| Mail host (primary MX) | Business domains with a definite answer | Accept every address |
|---|---|---|
| All business domains | 16,199 | 30.8% |
| Google Workspace | 4,060 | 42.0% |
| Other hosts, including security gateways | 4,901 | 40.3% |
| Microsoft 365 | 7,117 | 17.9% |
A domain counts as catch-all when our check of a random address on it was accepted. Google Workspace supports routing unknown addresses to a default inbox, and many small businesses turn it on. Security gateways (Proofpoint, Mimecast, Barracuda and similar) often accept at the edge and decide later, which pushes the "other hosts" share up. 121 more domains had no MX record or failed DNS when we classified them on 25 October 2026; they count in the "All business domains" row and have their own row in the CSV.
Microsoft 365 domains were the least stable. 221 of the 1,273 Microsoft 365 domains that accepted a random address also gave a definite "exists" or "not found" for other addresses in the same two weeks. On Google Workspace that happened on 2 of 1,705 domains, and on other hosts on 3 of 1,976. So a single catch-all reading on a Microsoft 365 domain is weaker evidence than the same reading on Google Workspace.
How often guessed addresses exist
| Mail host | One spelling: checked | One spelling: existed | Guessed pattern: checked | Guessed pattern: existed |
|---|---|---|---|---|
| All answering business domains | 12,758 | 37.4% | 70,580 | 1.6% |
| Google Workspace | 1,953 | 15.7% | 17,730 | 0.3% |
| Microsoft 365 | 5,870 | 29.8% | 37,314 | 2.1% |
| Other hosts | 4,845 | 55.2% | 14,982 | 1.7% |
These are business domains that answer mailbox checks honestly (not catch-all), where "exists" and "not found" come from the receiving server itself. Two spellings of one name existed 47.9% of the time (1,180 addresses), usually a real address plus one variant. Across all 84,518 addresses at answering business domains, 7.6% existed, because guessed patterns made up 83.5% of them.
What this means for a list: a finder or permutator that tries 10 to 16 patterns per person will hand you mostly addresses that do not exist. On a domain that answers, a verifier can sort those out. On a catch-all domain, the same guesses all come back "accepted", which is why a guessed list on catch-all domains is the riskiest thing you can send to. Our catch-all scoring page shows how we grade those rows using this kind of evidence, and we never call them valid.
What we did not publish
We set out to report what share of uploaded B2B list rows are catch-all, invalid, disposable or role-based. After removing the excluded data below, only 14,345 list rows from 9 accounts remained, and one account supplied 97.7% of them. A profile of what is, in effect, one customer's list is neither a benchmark nor anonymous, so we left it out. We will publish that split when enough independent lists exist.
Method
- Source. Every unique address with an SMTP answer in SimpleVerifier's 14-day result cache (checked 11 October 01:37 UTC to 25 October 03:50 UTC, 2026), plus the rows of bulk verification jobs created 21 to 25 October 2026. The cache holds one answer per address, the latest. Checks come from CSV uploads, the API, the email finder and the free email checker.
- Excluded. One account that showed card-testing payment behaviour and uploaded 1,000,000 rows in 10 lists on 23 October 2026, and 14 internal or test jobs. Every address appearing in an excluded job was removed from the cache data too (1,000,055 addresses removed in total). What remained: 119,294 unique addresses on 21,900 domains.
- The check. Our production checker looks up MX, connects on port 25, gives
MAIL FROMandRCPT TO, reads the reply and disconnects beforeDATA. Nothing is sent. A domain is catch-all when a random address on it is accepted. - Mail host. The primary (lowest preference) MX record, looked up on 25 October 2026: Google Workspace (
google.com/googlemail.comhosts), Microsoft 365 (mail.protection.outlook.com), and everything else. Consumer mailbox domains (Gmail, Yahoo, Outlook.com and similar) are excluded from the domain and existence tables; they are in the CSV. - Guessed pattern. On each domain, we grouped addresses that spell the same two-part name differently (16 common forms such as
first.last,flast,firstl,first,last.first). An address is "guessed" when at least two other spellings of the same name were also checked on that domain. - Privacy. The analysis ran on our own server. Only counts and shares left it. No address, domain or account identifier is in this report or the CSV.
How this differs from our earlier study of 51 mailbox providers: that one tested consumer providers with made-up addresses we generated. This one is about business domains, from real check volume.
Limitations
- Not a random sample. These are the addresses SimpleVerifier users chose to check over two weeks, heavily weighted by email-finder runs. Shares for "all business domains" depend on that mix; the per-host shares and the guessed-versus-one-spelling gap are the more portable findings.
- "Existed" is not "delivered". It means the receiving server accepted the mailbox at check time. We have no bounce data, so this is not a bounce rate.
- One checking server. All checks came from one server and IP. Providers judge the checker as well as the question, and a different server can get different answers.
- Catch-all can change. A domain can switch catch-all routing on or off, and Microsoft 365 answers in particular varied within the window.
- Classification at one date. MX records were read on 25 October 2026; a domain that moved hosts during the window is classed by its host on that date. A few hundred domains had no MX record or failed DNS at that moment; they are grouped as "No MX / DNS failed".
- Some own traffic may remain. Single checks through the free tools and API are not tied to an account in the cache, so a small number of our own test checks could be included. Known internal jobs were removed.
- Short window. Two weeks of data, October 2026. We plan to rerun this with a new date.
Download the data and embed the charts
Download the CSV (38 rows of aggregates: table, segment, metric, value, sample size). Licensed CC BY 4.0: reuse it with a link back to this page.
To embed a chart, paste one of these snippets. Each image links back to this page, which is the attribution the licence asks for.
Catch-all domains by mail host:
<a href="https://simpleverifier.com/blog/catch-all-domains-b2b-lists-2026"><img src="https://simpleverifier.com/data/studies/charts/catch-all-domains-by-mail-host-2026.svg" alt="Share of business domains that accept every address: Google Workspace 42.0%, other hosts 40.3%, Microsoft 365 17.9% (SimpleVerifier, Oct 2026)" width="680" style="max-width:100%;height:auto"></a>
<p>Source: <a href="https://simpleverifier.com/blog/catch-all-domains-b2b-lists-2026">SimpleVerifier, Catch-all Domains in B2B Lists, 2026</a></p>
How often guessed addresses exist:
<a href="https://simpleverifier.com/blog/catch-all-domains-b2b-lists-2026"><img src="https://simpleverifier.com/data/studies/charts/guessed-address-existence-2026.svg" alt="Guessed-pattern email addresses existed 1.6% of the time, against 37.4% for one spelling (SimpleVerifier, Oct 2026)" width="680" style="max-width:100%;height:auto"></a>
<p>Source: <a href="https://simpleverifier.com/blog/catch-all-domains-b2b-lists-2026">SimpleVerifier, Catch-all Domains in B2B Lists, 2026</a></p>
To cite it in text: SimpleVerifier (2026), "Catch-all Domains in B2B Lists, 2026", https://simpleverifier.com/blog/catch-all-domains-b2b-lists-2026.
Common questions
What share of business email domains are catch-all?
In SimpleVerifier's aggregate check data from 11 to 25 October 2026, 4,994 of 16,199 business domains that gave a definite answer (30.8%) accepted a made-up address, so their mailboxes cannot be confirmed by an SMTP check. The share was 42.0% for domains hosted on Google Workspace, 17.9% on Microsoft 365 and 40.3% on other hosts, including security gateways.
Do guessed email addresses (first.last, flast and so on) usually exist?
Rarely. When three or more spellings of the same person's name were checked at a domain that answers mailbox checks, 1.6% of those guessed addresses existed (70,580 addresses). Addresses checked in only one spelling existed 37.4% of the time (12,758 addresses).
Is a catch-all address valid?
Not confirmed. A catch-all domain accepts every address at check time, so a real mailbox and a typo get the same answer. SimpleVerifier marks these risky, never valid, and shows the evidence it has. See our catch-all scoring page for the signals and their measured hit rates.
Where does this data come from?
From aggregate results of mailbox checks run through SimpleVerifier between 11 and 25 October 2026, with one card-testing account's 1,000,000-row upload and our internal test jobs removed. No address, domain or customer is identified in the report or the CSV.
Can I reuse the data and charts?
Yes. The CSV and both charts are licensed CC BY 4.0: free to reuse with a link back to this page. Each chart has a copy-paste embed snippet on this page.
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