Hello @CarolineR596 ,
Do you have one email address column or multiple in your contact list? When uploading the list file, do the first 5-10 contacts all have an email address in the email address column? Is your list file one single page, or do you have a cover page or some other non-contact page in the file?
Overall, I'd recommend making sure your contact file is formatted properly for our system to be able to read. If you're still having trouble, please call general support or reply to the automated @ mention email you receive from my response, so we can securely collect the contact file and troubleshoot it.
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