To make sure the CSV will work as expected when uploaded, it must be subjected to a few validations on a row-by-row basis:
The uploaded file must be a .CSV and no other format.
The uploaded CSV must contain at least 1 row (i.e., not empty).
Each email should be in a separate row with an email format. Rows that are not emails will be skipped.
Duplicate emails will be counted once.
The file size limit is 5MB and 100K e-mail entries.
Email character limit to be 254.
And that's it. Once the file is uploaded, the dashboard will take care of the rest!