Most email list cleaners charge per email. Upload a few thousand contacts and the cleanup step becomes a budget line item instead of basic hygiene.
MailCull is built differently. You upload a CSV in Verify List, MailCull runs a full verification stack across every address it finds, and you export a cleaner list when you are ready. No credits to buy. No credit card required to start. No expiring trial language to decode.
What "free" actually means here
The MailCull Free plan includes 1,000 list-verification rows per month. That means you can run up to 1,000 addresses through the full check stack — and export the results — without paying anything.
There is no trial period. The free tier does not expire after 14 days or revert to a locked state. It just resets each month.
For teams that run occasional verification — before a campaign launch, after importing a new list, before a cold-outreach push — the free tier is often enough to build the habit without committing to a subscription first.
When you need more volume, Pro ($19/month) covers up to 100,000 list-verification rows per month. Scale ($49/month) extends that to 500,000 rows.
What MailCull actually checks
This is the part that differs from many tools that describe themselves as "list cleaners" but stop at surface-level checks.
Syntax validation
Catches structurally broken addresses: missing @ signs, invalid characters, malformed domains. Every tool does this. It eliminates the clearly broken addresses quickly.
Domain and MX records
Confirms the domain exists and has MX records configured to receive mail. If a domain has no MX records, mail cannot be delivered to any address on it — regardless of what the mailbox name is. Reliable negative signal.
Typo detection
Flags addresses on domains that look like common provider misspellings: gmial.com instead of gmail.com, yahooo.com, outloook.com. These are almost always data entry errors.
Disposable and role address detection
Identifies temporary inbox services (Mailinator, Guerrilla Mail, and similar) and role addresses (info@, noreply@, admin@, contact@) that exist but are not suitable for most sending workflows. Role addresses reach shared inboxes rather than individuals. Disposable addresses expire.
SMTP mailbox verification
This is the layer that catches the largest share of bad addresses that pass the checks above.
MailCull's engine opens a direct SMTP connection to the mail server, performs an EHLO handshake, presents a MAIL FROM, and issues RCPT TO for the specific address being verified. The server's response tells you directly whether that mailbox exists:
- 250 OK — the server is willing to accept mail for this address
- 550 User unknown (or similar 5xx) — the mailbox does not exist; delivery would hard-bounce
- 450 / 452 — temporary deferral; the verdict is inconclusive (greylisting or rate-limiting)
The engine performs an opportunistic STARTTLS upgrade when the receiving server supports encryption, matching the behaviour of a real sending mail server. Servers that require a properly configured HELO hostname and MAIL FROM domain — increasingly common as an anti-abuse measure — get both.
Microsoft 365 HTTP enumeration
M365 is the dominant business email platform. It is also the most common source of false positives in SMTP-only verification tools.
Microsoft's Exchange Online Protection layer accepts RCPT TO for any address on an M365 tenant — even completely non-existent ones — and generates non-delivery reports internally. An SMTP probe against an M365 domain returns 250 OK for a real mailbox and 250 OK for a made-up one. They look identical.
MailCull handles this by running a three-step HTTP cascade using Microsoft's own authentication endpoints before the SMTP probe:
- GetUserRealm — confirms whether the domain routes to M365
- GetCredentialType — checks whether this specific username has an active M365 account
- Autodiscover v1 — cross-references account presence
When the cascade confirms an active account and SMTP agrees, the verdict is high-confidence deliverable. When they disagree — which happens on some hybrid or federated tenants — MailCull returns risky with a m365_smtp_disagreed reason rather than committing to an unreliable verdict.
For any list with a significant B2B component, this M365 handling makes a real difference in result accuracy.
Catch-all detection
Some domains accept all RCPT TO commands regardless of whether a real mailbox exists, routing everything internally. A verifier that does not detect this will mark all addresses on catch-all domains as deliverable — including non-existent ones.
MailCull probes catch-all behaviour by sending a RCPT TO with a random, implausible local part. If the server accepts it, the domain is flagged as catch-all and individual addresses on that domain are marked risky rather than deliverable.
The four-status output
Every address in a verified list comes back with one of four statuses:
- Deliverable — the mailbox passed the full check stack with no overriding negative signals
- Risky — technically present but with signals that suggest caution: catch-all domain, M365 cross-check disagreement, role address, greylisted response
- Undeliverable — confirmed non-existent (SMTP 5xx) or domain with no valid MX records
- Unknown — the server did not give a conclusive answer (timeout, connection refused, policy block without specifics)
These four buckets give you something to act on. Deliverable rows go into the campaign. Undeliverable rows get cut. Risky and unknown rows require a judgment call based on how much risk your use case tolerates.
The Verify List workflow
- Export your list as a CSV. Any format works — multi-column files with names, companies, phone numbers, and other fields alongside email addresses are fine. MailCull extracts the addresses it finds.
- Upload to Verify List. The engine starts processing immediately.
- Review the status breakdown. You see a summary of how addresses distributed across the four buckets. A healthy list from a good source might be 85-90% deliverable. A list from a mixed or older source might be 60-70%. You know within seconds where you stand.
- Filter and export. Choose which status buckets to include in your export. The result is a clean CSV ready to import into your sending tool, CRM, or ESP.
Why the per-email pricing model creates a bad habit
Per-email pricing makes verification feel like an event rather than maintenance. When every run has a dollar cost, teams delay verification until a bounce problem forces them to run it urgently.
The cost compounds:
- Lists go unverified for months while decay accumulates
- A campaign goes out with a noisy list, bounce rates spike, domain reputation takes a hit
- The cleanup becomes expensive to run and slow to recover from
When verification is free and repeatable, teams run it more often:
- Before every campaign
- After importing an old database
- Before a cold-outreach push
- When migrating to a new ESP
That frequency is what actually protects sender reputation. It is not about squeezing marginal accuracy gains out of a single verification run. It is about making the verification step cheap enough that it always happens.
Who MailCull fits
MailCull is a good fit for:
Agencies cleaning client CSVs. You get a consistent, repeatable workflow that does not require per-client billing math. Import, verify, export, deliver to client.
Newsletter and marketing operators managing older segments. Even opt-in lists decay at roughly 2% per month. A quarterly verification run prevents slow accumulation of bounceworthy addresses.
Sales and RevOps teams reviewing prospect files. Before a cold sequence goes into Smartlead or Instantly, a verification run removes the rows most likely to damage domain reputation.
Operators migrating between tools. Database imports and CRM migrations are exactly the moments when stale, duplicate, and malformed addresses surface. Verify before you import.
Developers testing email workflows. The single-check tool — available on the Free plan for quick tests, with 100 deep-scan credits per month for Pro-level probing — makes it easy to validate specific addresses during development without a full list upload.
What MailCull is not
MailCull does not write or send email. It is a verification tool, not a sender. The output is a clean list you take into your existing sending workflow.
MailCull is not optimised for extremely high-volume users who need millions of verifications per month on tight per-credit economics. For that scale, the pricing math eventually favours a purpose-built high-volume platform. The Scale plan at $49/month handles 500,000 rows per month — that is the ceiling before you would need to contact us about a custom arrangement.
MailCull is for teams where verification is a regular part of the workflow but not the core business operation.
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