If you are previewing an email that has dynamic data you are able to view by Person which is the email address. It would be helpful to be able to view by ID in case the email is tied to multiple IDs (which is on purpose). This is helpful when you are testing an email that have velocity coding and dynamic data. Marketo currently pulls the first email address that it finds on the system and if that lead id does not qualify for the campaign the dynamic data would show as blank in the email preview.
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