Create Duplicate Marketo New Leads Sync to Salesforce

2. Therefore, the other way I'm considering is to fill-in email address field with other text and put the real email address in a backup field and replace it after salesforce sales turns it to opportunities. But in this ways, web tracking seems will be separated.

 

Working with duplicate leads is always (at least in the most cases) tricky. In the above quoted method, I think it'd be difficult to associate form fill activity to the correct lead in-case they fill multiple forms/same form multiple times. An alternate way is to have the custom de-duplication rules set up in your Marketo instance i.e., use a compound de-duplication key for creating and associating respective activities to correct people with same email address in Marketo, for this you'd want to have all the de-duplication fields present on the form/list import, etc. You can also choose to have seperate custom de-deplication rules for differet sources (i.e., List Import, Web Form fill out, etc.). One thing to note here is that the Email Address needs to be one of the fields in the compound de-duplication key. A major caveat with this approach is that if not being properly handled this can easily create a lot of duplicate record and in-accurate data in your database. 

Plus, once the leads has pass to salesforce, sales wish that we will not update any customer data afterwords.

(For now, if the customer submit different name with the same email, the data will be updated.) 

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You can choose to block fields you would not like to get updated from the respective input sources from the field management section in the Marketo Admin, but that'll apply to all people, and not just the synced records with the SFDC. Additionally, you can think about adjusting the permissions for the Marketo sync user in the SFDC, but I don't think there's an field level block update permission available in SFDC (AFAIK - you have read and edit permissions on the fields, and you'd need to grant both of these permissions to the sync user for the respective fields you'd want to sync over the data to when a lead is created by Marketo in the SFDC).