When I do a mass delete in marketo it is synching with salesforce and therefore creating leads again in marketo. How do I stop this from happening?
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To prevent this, you need to set up a sync filter. See Restricting Leads from Syncing to SFDC With Sync Filters .
Then once this is done, read this to learn how it really works.
Finally, the way to handle "desync" before deleting a lead in Marketo is explained here: "Sync with Marketo" mysteries part 2
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