Comprehensive result code & credit matrix
The table below provides a complete reference of MailCheckup's status outcomes, underlying reason codes, credit charges, and operational recommendations:
| Result Classification | Diagnostic Reason Code | Credit Charge | Mailbox Certainty | Operational Recommendation |
|---|---|---|---|---|
| Deliverable / Valid | SMTP 250 2.1.5 Recipient OK | 1 Credit | High certainty | Safe for all campaigns and workflows |
| Undeliverable / Invalid | SMTP 550 5.1.1 / DNS NXDOMAIN | 1 Credit | Definite invalidity | Suppress immediately to stop bounces |
| Catch-All / Accept-All | Domain-wide catch-all policy | 1 Credit | Domain yes; inbox uncertain | Hold for warm-up or verified contacts |
| Disposable / Burner | Blocklist match (97k trie) | 1 Credit | Temporary inbox | Exclude from trial and onboarding forms |
| Role Account | Prefix match (info@, sales@) | 1 Credit | Shared group alias | Use for B2B billing; avoid in 1-to-1 cold outreach |
| Mailbox Full | SMTP 452 / 552 Over Quota | 1 Credit | Inbox overfilled | Hold and recheck in 7–14 days |
| Unknown / Inconclusive | SMTP 451 Greylisted / Timeout | Free ($0.00) | Inconclusive | Do NOT delete. Re-verify later for free |
The critical distinction: Unknown vs Invalid
One of the most expensive mistakes marketing teams make is deleting unknown rows. An invalid address failed technical checks; an unknown result means the destination server deferraled the probe (greylisting), timed out, or blocked port 25 interrogation. The mailbox itself may be perfectly active. Leave unknown rows in your list and re-verify them later for free.
Managing the Risky segment (Catch-all, Role, Disposable)
Summarized reports group catch-all domains, role accounts, disposable inboxes, and over-quota mailboxes under the label 'Risky'. This is an advisory categorization. For example, role accounts (billing@, sales@) are entirely acceptable for B2B invoicing, whereas disposable emails should be pruned from lead funnels.
CSV export column structure & joins
MailCheckup preserves your original CSV data intact. When you export results, we append five structured fields: mcu_status, mcu_reason, mcu_smtp_code, mcu_checked_at, and mcu_charged. You can easily rejoin the verified export back into HubSpot, Salesforce, or your custom database using your source record ID.
Frequently asked questions about results
Why is an unknown result not the same as invalid?
An unknown result indicates that the remote mail server did not provide a definitive yes or no answer (often due to temporary greylisting, anti-spam rate limiting, or connection timeouts). The address may be perfectly deliverable. Deleting unknown records artificially destroys valid sales opportunities.
Why does MailCheckup classify catch-all domains separately from deliverable?
Catch-all domains are configured by IT administrators to accept emails sent to any string @company.com. Because the server answers 'yes' to everything, an external verification tool cannot confirm whether that specific human inbox exists. Marking catch-all as deliverable misleads senders and risks spam complaints.
What is the 'Risky' segment in summarized reports?
Risky is an operational grouping comprising catch-all domains, disposable addresses, role-based accounts, and full mailboxes. It is not an independent charge; each component is billed at standard unit rates (1 credit) and separated in your CSV export for tailored sending policies.
How do I re-verify unknown addresses later?
In the customer portal at cp.mailcheckup.net, open your list, filter by the 'unknown' segment, and click 'Re-verify segment'. Our dialers will re-attempt connection. Any addresses that remain unknown still cost $0.
Does deliverable verification mean the email will avoid the spam folder?
No. Deliverable proves that the destination mail server accepted the mailbox probe during verification. Whether your actual campaign reaches the primary inbox depends on your SPF/DKIM/DMARC authentication, sender domain age, email copy, and recipient engagement.
What happens to credits if I cancel a list run before completion?
Checks that already finished remain billed and saved in your report. Any reservation holds on unverified or in-progress rows are immediately released back to your available credit balance.