What the check does
An email verification service asks a short sequence of questions. A later step is skipped when an earlier one already answers. The same order is written out on how the check works, and the plain-language version is on what email verification checks.
Syntax
Broken syntax is invalid. A common typo can come back as a suggestion. The suggestion is separate. The address you submitted is not rewritten.
Disposable and role
Disposable domains and role addresses such as info@ or support@ are classifications. They are not a syntax failure. Disposable email detection is its own decision.
Mail routing
No MX record, or a mail server that cannot be reached, is inconclusive. It is not invalid, and it is not a confident statement that the person does not exist.
Mailbox response
Accept means deliverable. Reject means undeliverable. Accept-everything means catch-all. A full mailbox means mailbox full. Greylist, a block, a timeout, or no answer means unknown. RFC 5321 is the SMTP definition of those replies. MailCheckup keeps the difference. It does not turn a timeout into a rejection.
What each result means
One finished chargeable result costs one credit. Inconclusive results are free. Risky is a summary of disposable, catch-all, role account, and mailbox full. It is not a separate charge. The same codes, with the same credit rule, are on the results guide.
| Result | What it means | Credit |
|---|---|---|
| Deliverable / valid | The server accepted this recipient. That is not inbox placement. | 1 credit |
| Undeliverable / dead / invalid | The server rejected the recipient, or the syntax is broken. | 1 credit |
| Catch-all | The domain accepts every address. It is not marked deliverable. | 1 credit |
| Disposable | A throwaway domain. Kept separate so you can leave it out. | 1 credit |
| Role account | A shared address such as info@ or support@. | 1 credit |
| Mailbox full | The mailbox cannot take more mail right now. | 1 credit |
| Unknown | No clear yes or no. Unknown is not invalid. | Free |
| Retry later | The server asked for another try. | Free |
| Greylisted | The server deferred the check. | Free |
| Mail server unreachable | No MX, or the server could not be reached. Not invalid. | Free |
| Provider blocked | The provider blocked the check. | Free |
| System error | The check did not finish. The hold is released. | Free |
| Not checked | No finished result yet. | Free until a chargeable result exists |
Catch-all is not deliverable. Read catch-all email verification and why a catch-all domain stays uncertain. Unknown is not a bad address. The difference is on unknown versus invalid.
What you pay
Free is $0 and includes 100 credits, enough to see one list. The usual first purchase is 5,000 credits for $15. Pack credits do not expire. Monthly plan credits expire at the end of the paid period and do not roll over. Which results cost a credit is in the table above. You pay only when the answer is finished.
Other pack and plan prices are on pricing. Paid checkout runs in the app. Credits appear after Stripe confirms payment. The invoice is issued by Secuno LLC and downloaded from Billing. Product help is support@mailcheckup.net. Invoice questions go to billing@mailcheckup.net. The contact page lists both.
How a list runs
This is bulk email verification for a file you already have, and how to prepare the CSV before you upload it. You can also paste addresses. When the run finishes, export CSV, TXT, or XLS. Reading the report is a separate step from deciding who receives the campaign.
Duplicates in one file are stored once. They are not checked twice and they are not billed twice. A running list can take more addresses. They join the same run. You do not need a second list, and you do not need to wait until the current rows finish.
Remove, clear, and delete are refused while a list is importing or verifying. Stop first. Stopping releases holds on checks that never finished. Credits already consumed stay consumed. A recheck of one group, such as unknown or mailbox full, can use another credit because it is a new finished check. Results already saved for the rest of the list stay.
What the result does not decide
Deliverable means the mailbox server accepted the recipient during the check. It does not mean the message will reach the inbox, and it does not mean the person will read it. Unknown means the server did not answer clearly. Deleting those rows treats a missing answer as a bad address.
Verification is not consent, and it does not prove the person owns the inbox. A deliverable address can still be someone who unsubscribed or never agreed to hear from you. Keep suppression and permission in the tool you send from.
The sample checker on this marketing site does not contact mail servers. A real check runs from the app at cp.mailcheckup.net. If you want the same check inside another system, start with the email verification API. The docs on this site are integration principles, not an executable REST contract. Lists can also be checked from an agent through the MCP server, or pushed to your own URL with webhooks. File handoffs and the limits of connectors are on integrations.
Questions
Is unknown the same as invalid?
No. Unknown means the mail server did not give a clear yes or no: greylist, a block, a timeout, or no answer. No MX, or a server that cannot be reached, is also inconclusive. Those results are free. Invalid means the syntax is broken, or the server rejected the recipient, and that result costs one credit. Leave unknown rows in place, or recheck that group later.
Is catch-all the same as deliverable?
No. Catch-all means the domain accepts every address. MailCheckup does not mark that deliverable. Deliverable means the server accepted this recipient. A catch-all domain did not prove that one mailbox exists. Catch-all costs one credit. It sits in the risky summary with disposable, role account, and mailbox full. Risky is not an extra charge.
Does checking an address send an email?
No. The check asks the mail server about the recipient. It does not send your campaign, and it does not place a message in the inbox. The sample on this website does not contact mail servers at all. A real check runs from the app.
Does a deliverable result guarantee the inbox?
No. Deliverable means the mailbox server accepted the recipient when asked. Inbox placement still depends on how you send, authentication, reputation, and the message. Verification is also not consent. A deliverable address can belong to someone who never agreed to hear from you.
Which results use a credit?
One credit for a finished chargeable result: valid, deliverable, undeliverable, dead, invalid, disposable, catch-all, role account, and mailbox full. Free: unknown, retry later, greylisted, mail server unreachable, provider blocked, and system error. Free signup is 100 credits. The usual first purchase is 5,000 credits for $15. Pack credits do not expire. Monthly plan credits expire at the end of the paid period and do not roll over.