The standard Marketo configuration uses the Email and ID fields to determine if a lead is duplicate.  The TIBCO Scribe® Online Connectors for Marketo REST and Marketo SOAP use the Marketo APIs and, therefore, also follow these same rules when using Upsert to create or update lead data in Marketo.  If your source data does not contain information that is compatible with these two fields, you may need to use an alternate method of determining duplicates.

Alternate Deduping Method
 

Maps using Marketo SOAP as a target can be configured to use a different field to meet deduping requirements.  When using an Upsert Block, go to the Fields tab and map a unique source field to the Marketo ForeignSysPersonID field.  Mapping to the ForeignSysPersonID field supersedes Marketo’s default deduping logic and uses this single field for deduping instead.

For additional information, see the following in the TIBCO Scribe® Online Help:  TIBCO Scribe® Online Connectors For Marketo
 
 

How to force deduping against different standards of Marketo