I have recently come accross the problem of recieveing an attendee list from a tradeshow in which the leads don't have an email address. I want to upload the list and tie it to a Marketo campaign before pushing it thorugh to our CRM. Will the lack of an email cause a problem?
Since Marketo uses email address as a unique identifier, there is no way for you to later update those records. Unless someone in your CRM updates them to add email addresses. Without an email address, they are lost to Marketo, although Marekto can create the records and sync them to CRM.
So lets say your list today has Joe Smith, CTO, Acme Corp. If tomorrow you upload a list or Joe Smith fills out a form, Joe Smith, CTO, Acme, firstname.lastname@example.org will become a duplicate new record.