When importing subscriber data for multiple value custom fields, you'll need to format your file in a certain way to ensure the data is mapped correctly. This formatted basically involves the use of a double pipe separator (||) between your multiple value options.
Here's how data might look like when you import it from a CSV (Comma Separated Values) file.
Name, Email, Interests, Country
John Smith, john@smith.com, Surfing||Movies||Reading, Australia
By separating all your multiple options with a double pipe, we make it super easy to import your subscriber data and marry it up with the custom fields in your subscriber lists. We use the same formatting when you export your data as well, making it easy to export, make any changes you want and re-import back into the same or other lists.