Hi Michael, if this is a segmentation created in your Marketo, then you'll need to go into the Lead Databse, find that segmentation, and select "create draft". Once you have a draft, you can edit the choices that are available and define their smart lists. Once you approve, it can take some time for the entire database to resegment properly, so be sure to budget time for that to finalize before you want to use the field for a mailing or anything else.
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