In this case, the best way to navigate around this issue is to set up your Auto-Assignment rules in SFDC such that your leads are assigned to a Queue if they would otherwise be assigned to the User which is creating them. You can do this by adding a final rule to your assignmnt rules for leads with no criteria. When a lead is owned by a Queue, Marketo will not populate the owner email address, so you would be able to use this token: {{lead.Lead Owner Email Address:default=example@example.com}} For leads which have an empty Lead Owner Email Address, it will use the default.