Bulk Email Finder: Best Practices for CSVs

Overview of the Bulk Email Finder

Mailsfinder's Bulk Email Finder allows you to upload a CSV file containing a list of people and their companies, and receive verified email addresses in return. Instead of looking up contacts one by one, you can process thousands of records in a single upload. To get the best results, your CSV file needs to follow specific formatting guidelines.

Required Column Headers

Your CSV file must include at least the following columns. The column headers are case-insensitive, but they must match exactly (no extra spaces or special characters):

Sample CSV Template

Here is a correctly formatted CSV file that you can use as a starting template:

first_name,last_name,company,domain,linkedin_url,job_title
John,Smith,Acme Corp,acme.com,https://linkedin.com/in/johnsmith,VP of Sales
Sarah,Johnson,TechStart,,https://linkedin.com/in/sarahjohnson,Head of Marketing
Michael,Chen,,globaltech.io,,CTO

Notice that you can provide either the company name or the domain (or both). Providing both increases the accuracy of the lookup. If a LinkedIn URL is available, include it for the highest possible match rate.

File Size and Row Limits

Mailsfinder accepts CSV files with the following limits:

• Maximum file size: 10 MB per upload
• Maximum rows per file: 50,000 rows (excluding the header row)
• Maximum columns: 20 columns (extra columns are preserved in the output but ignored during processing)

If your file exceeds these limits, split it into smaller files and upload them separately. Each upload creates a separate job that you can track independently in the dashboard.

Encoding and Formatting Tips

Incorrect file encoding is one of the most common causes of upload failures. Follow these guidelines to ensure your CSV is processed correctly:

1. Use UTF-8 encoding. Save your file as UTF-8 (without BOM). Most spreadsheet applications default to this, but if you are exporting from Excel, choose "CSV UTF-8 (Comma delimited)" from the Save As dialog.
2. Use commas as delimiters. Mailsfinder expects comma-separated values. If your regional settings use semicolons, convert them to commas before uploading.
3. Quote fields containing commas. If a value contains a comma (e.g., "Acme Corp, Inc."), ensure it is wrapped in double quotes so the parser does not split it incorrectly.
4. Remove BOM characters. Byte Order Mark (BOM) characters at the start of the file can cause the first column header to be unrecognized. Use a text editor to strip BOM if needed.
5. Avoid merged cells and formulas. If you are exporting from a spreadsheet, ensure there are no merged cells, formulas, or hidden formatting. Export as a plain CSV.

Common Errors and How to Fix Them

• "Missing required column: first_name" -- Your header row is missing or misspelled. Check for trailing spaces or invisible characters.
• "Row 45: Invalid domain format" -- A domain value contains a protocol prefix (e.g., "https://acme.com"). Remove the "https://" and use just "acme.com".
• "File encoding not supported" -- Your file is likely saved in a non-UTF-8 encoding such as ISO-8859-1 or Windows-1252. Re-save as UTF-8.
• "Maximum row count exceeded" -- Your file has more than 50,000 data rows. Split the file into smaller batches.
• "Duplicate rows detected" -- Mailsfinder automatically deduplicates rows with identical first_name, last_name, and domain combinations. Duplicates are skipped and do not consume credits.

Summary

A well-formatted CSV file is the foundation of a successful bulk email finding job. Use the correct column headers, save in UTF-8 encoding, stay within the file size limits, and double-check for common formatting issues before uploading. Following these best practices will maximize your hit rate and minimize wasted credits.