Hi Don,
Thanks for your quick reply. We use Ringlead with SFDC to help prevent duplicates. We had a data dump from SFDC into Marketo where a lot of our leads are missing email addresses so we are afraid of importing list into Marketo and then having duplicates. I am trying to figure out the best way to move forward while dealing with the mess that my predecessor left me. 😉 I am not sure I could get approval to delete all the leads in Marketo that are missing email addresses, although that sounds like the way to go...