To make sure the CSV is useful to the user, the CSV 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 row must be written in an email format. Rows that are not emails will be skipped.
Duplicate emails will be counted once.
File size limit of 5mb and 100K maximum number of email cells.
Email character limit to be 254.