If you got an error when uploading a file to DataValidation when trying to check your email list, you will need to re-format your file and import again.
When you upload a list of emails that has been saved in a format [or encoding] that we do not currently support, you will get this format error. Our system currently accepts .csv format, but sometimes these accepted formats can still contain unsupported encoding (such as UTF-16).
Sometimes, an email list in the proper format can still contain non-english alphabet characters or other characters that our system will not accept. In many cases, unicode errors will cause the formatting to be off and the file will fail during import.
To fix this problem we recommend re-saving your .csv file with a UTF-8 encoding (instead of UTF-16 encoding) and then re-importing. The process for doing this varies depending on your spreadsheet editor (ie. Numbers, Excel, or TextEdit).
Consult the Help section for which editor you are using and attempt reloading to the DataValidation system. You will be able to upload and check the email list when using the properly formatted file.