Every form fill, signup, or customer registration brings new email data into your system. The quality of that data determines whether your campaigns reach real people or get stuck chasing empty inboxes.
One of the toughest challenges for teams is deciding what to do with addresses that standard checks can’t confirm.
Left unresolved, these records can drag down deliverability, inflate bounce rates, and waste time on contacts that never engage. But handled correctly, they can unlock new opportunities already sitting inside your lists.
In this guide, we’ll show what these hard-to-verify addresses are, why most tools miss them, how email validation API solves the problem instantly, and why many B2B teams trust Listmint to keep their data accurate.
A catch-all email address accepts all incoming emails, even if the specific mailbox does not exist. Instead of bouncing, the domain’s server routes every message into one inbox or a default location.
These addresses often appear on business domains. For example, if someone sends an email to a misspelt address like salesx@company.com, a catch-all domain will still accept it. That makes them different from standard email addresses, which return a bounce when the mailbox is invalid.
Catch-all addresses can make up a significant portion of B2B databases, with about 30% to 40% of business leads often falling into this category.
Without a way to validate them, companies risk sending messages that never reach an active reader. That creates higher bounce rates, weaker email deliverability, and wasted effort inside marketing campaigns.
Handled with the right verification process, these addresses can reveal valid contacts hidden in your existing lead list. Instead of treating them as unknown emails or risky emails, teams can identify which catch-all domains actually connect to real users.
On a catch-all domain, the mail server is configured to accept all emails sent to that domain.
During an SMTP handshake, the RCPT TO command often returns 250 OK for any local part, so a basic SMTP check cannot confirm a valid address for a specific inbox. That means single email verification over SMTP alone can’t reliably verify catch-all email addresses.
Because the server appears to accept all, many tools label these as unknown emails or risky emails. Teams then face a choice: avoid sending emails to protect sender reputation, or send and risk bounce rates that harm email deliverability.
Inbox providers closely monitor complaints. Gmail requires bulk senders to keep reported spam rates below 0.3% in Postmaster Tools, and Yahoo now enforces complaint thresholds and one-click unsubscribe for consumer mailboxes.
In short, an SMTP-only email verification process can’t confirm catch-all email addresses due to server behavior, and sending to unverified catch-all addresses can create deliverability and reputation issues under modern provider rules.
Catch-all verification API goes beyond surface checks and delivers clear results at the point of entry. Instead of waiting for a bulk email verification upload or cleaning lists after campaigns fail, Listmint’s API integration validates emails in real time.
When a new contact enters a form, CRM, or file upload, the verification process runs instantly. The Listmint API reviews the domain setup, server response, and related data points to separate valid emails from catch-all addresses.
Results are returned in simple categories: valid, invalid, catch_all_valid, and catch_all_invalid. That clarity allows teams to act on data immediately instead of guessing which addresses can be used.
Imagine a signup form on a website. As soon as an entry is submitted, the API can validate emails before they ever reach a lead list. Unknown emails or risky emails are flagged, helping avoid sending emails that cause high bounce rates or trigger spam traps.
The flexibility of an API means you can run a single email verification or process all the emails in bulk on one platform. That keeps records clean, improves open rates, and supports reliable email marketing campaigns.
Get started for free and test Listmint’s API on your email list.
A catch-all verification API gives teams reliable answers where standard checks fall short. Instead of marking catch-all addresses as unknown emails or risky emails, the API provides clear outputs that separate valid emails from those that only appear to accept all.
One of the main advantages is real-time API integration
A new address entering a signup form, CRM, or lead list can be validated instantly before it impacts sender reputation. That means campaigns avoid sending emails to addresses that trigger high bounce rates or spam complaints.
For larger datasets, the same process supports a bulk email verification upload. Marketing teams can process all the emails in a file or database at once, cleaning data before launching email marketing campaigns.
Sales operations benefit too, since every valid address is preserved for outreach instead of being lost to over-cautious filters.
APIs also bring flexibility. Teams can run single email verification checks during live campaigns or schedule batch jobs across multiple systems in one platform. Developers gain secure access through API keys, logs, and SDKs that make integration straightforward.
With these advantages, an API is the most efficient tool for turning catch-all addresses into reliable data that strengthens the entire email marketing strategy.
Listmint is purpose-built to solve the toughest challenge in the email verification process: validating catch-all addresses in real time. While other services label them as unknown emails or risky emails, Listmint provides clear results through its dedicated API.
With more than 1B emails verified and consistent 99%+ accuracy, the platform delivers answers teams can trust at scale.
In recent catch-all benchmarks, teams saw an average 84% valid rate on catch-all addresses compared to about 55% with generic verifiers, based on internal tests across mixed B2B lists.
B2B marketers and sales operations use Listmint to validate emails directly in signup forms, CRMs, and bulk email verification uploads.
The outputs classify addresses as valid, invalid, catch_all_valid, or catch_all_invalid, giving teams instant clarity. That level of detail helps recover safe contacts hidden in lead lists and prevents bounce rates that harm email reputation.
Enterprise clients, SaaS platforms, and agencies rely on Listmint for more than speed. The service includes detailed reporting by workspace, showing pass rates, status breakdowns, and usage volume.
Data is encrypted during transport, API keys are scoped for security, and all records are automatically removed on a set schedule, keeping compliance and trust at the center of every integration.
With proven reliability at scale and advanced support for catch-all email verification, Listmint stands out as the trusted tool for teams serious about data quality. Over 50% more valid addresses can be reclaimed from existing lead lists compared to standard verification methods.
Email data shapes the success of every campaign. Records that cannot be confirmed slow teams down, weaken performance, and create unnecessary risk. The right tools change that outcome.
With a reliable email verification API in place, teams can focus on engaging real people instead of sorting through uncertain data. More usable contacts mean stronger campaigns, better deliverability, and confidence in every send.
Listmint makes this process simple and proven at scale. Trusted by SaaS platforms, agencies, and enterprise teams, it delivers instant results backed by billions of verified emails.
Get started today with a free account and see how much hidden value exists inside your data.
Catch-all email addresses that belong to domains that accept all incoming emails, even if the specific mailbox does not exist. A catch-all verification API identifies if these addresses are valid or invalid so teams can avoid sending emails that create bounce rates or harm sender reputation.
Yes. Teams can process thousands of records through a bulk email verification upload. The verification process separates valid emails from unknown emails, giving marketers a clean lead list before starting new email marketing campaigns.
API integration lets validation run in real time as addresses enter forms, CRMs, or files. It lowers the risk of spam traps, avoids risky emails, and protects your sending reputation across campaigns. You can start with a free account to test the flow before rolling it out to the team.
