Upload file for verification

Upload a file containing email addresses for asynchronous batch verification.

Supported formats:

• CSV (.csv)
• Excel (.xlsx)
• Text (.txt) - one email per line

Limits:

• Maximum file size: 20 GB (aligned with the web uploader)
• No application-enforced row-count limit

Large uploads: small files are parsed synchronously and the response includes email counts. Files above the inline-parse threshold are accepted and prepared asynchronously: the response returns status: preparing without counts, and clients poll status_url for progress and counts.