Hi @bbeamish
Not sure I understand the topic, when you upload a file, you can use the Line Number as an ID

Will you store these email is Recipient or maybe Visitor or do you just want to send a message to these emails and not store anything against these emails. You could use ExternalFile as Target Mapping to send emails from a file without recipient or visitor records, if you do so, you would not have any history associated to these deliveries.
Hope this helps,
Thanks
Denis