We have a list of older "legacy" data from trade shows that predates our Marketo subscription. We want to upload the list to Marketo but know that there is some overlap with data that is already in the our Lead Database.
Can someone please confirm that one way to avoid unnecessary duplication would be to upload ONLY the email addresses from the legacy list? If not, alternative suggestions are welcome.
I'm not entirely sure this answers your question, but when you import a list, we de-duplicate on email address. Check out this article on the different modes we have for import.
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