Leads are created on our Marketo from two sources - Salesforce.com and Web API. In an ideal situation, if a lead exists on Marketo and if another source tries to create the lead using the same email address, it should sync data to existing profile instead of creating a new duplicate lead profile with same email address. We have accumulated thousands of such duplicates and they continue to add up every day.
Here is a visual representation of this problem:
I'd love to know if the community has any ideas and best practices that can help us resolve this problem.