no column with email addresses
Name the column with --column, for example --column "Email Address".
column appears twice
Rename one of the two columns in the export.
mail_domain says unknown
The DNS lookup timed out or you are offline; the address is left as it was. Run again later.
a real company domain is flagged as a typo
Add it to an --allowlist file.
Claude does not use the skill
Check it is switched on in Settings → Capabilities → Skills, then name it in your message.
The script says a column is missing
Rename your header to one of the names in README, or say the mapping in your message.
Code execution is off
Skills with scripts need code execution enabled in Claude.ai settings.
FAQ
Is this the same as a paid email verification service? It covers the checks that do not need a mail server: syntax, typos, duplicates, role and throwaway addresses, your suppression list and whether the domain can receive mail. It does not probe individual mailboxes, so it cannot spot a deleted mailbox on a working domain.
Does it send my list anywhere? No. With --check-mx only the domain names are looked up over DNS-over-HTTPS. Without it nothing leaves your computer.
Which file formats work? CSV with commas, semicolons, tabs or pipes, from any email tool, CRM or form, or a plain text file with one address per line. The email column is found automatically or named with --column.
Can I merge several lists? Yes. Give several files; the email columns are merged into one and duplicates across files are caught.
What should I do with risky addresses? Review them. Role inboxes and throwaway domains often never opted in. Use --keep-risky to keep them in clean.csv.