What is the maximum file size for a bulk upload?

The hard cap on a single bulk upload file in Valid Email Checker is 100 megabytes. This is checked client-side the moment you drop a file onto the upload form. Anything above 100 MB is rejected immediately, before a single byte is sent to our servers, with a toast that reads "File size exceeds 100MB limit. Please upload a smaller file."

What 100 MB actually fits

For context, 100 MB is a lot of email addresses. A plain TXT file with one email per line averages about 25 to 35 bytes per address (an email plus a newline), so 100 MB holds roughly 3 to 4 million addresses on paper. The practical email count limit is the other constraint that kicks in first: 1,000,000 addresses per task. Both limits are checked, and whichever you hit first is the one that blocks the upload.

When a CSV exceeds the limit

CSV files are larger than plain TXT because every row carries the email plus extra columns (names, signup dates, sources, custom fields). A CSV with 500,000 rows and a dozen columns can easily land at 50 to 80 MB. If your export came back near the cap, here are the levers:

• Strip columns you do not need before exporting. We preserve every column you ship in, so trimming pre-upload is the simplest fix.
• Save as CSV instead of CSV UTF-16 BOM. Excel sometimes defaults to wider encodings that double file size.
• Open the CSV in a text editor and check for stray quoting or excess whitespace adding bulk.
• Split the file into two or three pieces and upload them as separate tasks.

Why the limit exists

Files of this size are read entirely into memory in the browser when we parse them for the email count and preview. Going above 100 MB risks tab freezes on lower-memory devices and timeouts on slower connections. Splitting the work into multiple sub-100 MB uploads keeps the UI responsive and the server-side pipeline predictable.