De-Duping from SFDC campaign when I import a list

[Anonymous]

A few members of my team recently attended a conference. They have put the business cards that they collected into the campaign. Later on today, I will recieve a list of TOTAL conference attendees and I need to add them to our Marketo Database. 2 things need to happen

1-I need to upload this list into our database and de-dupe (so that there are no new leads created for those that we already have in our database)

How do I do this?

[Anonymous]

Marketp de-dupes on the way in based on the primary key of "Email Address" s you should be OK here...