Get the owner email address

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We need to get the owner's email address in the BML that sets the default value for the Text Attribute.
However, from the system variable name that can be selected in Select Attributes, it seems that while we can get the value of _system_user, we cannot get the value of owner.
It's important to note that what we want to get is the owner's email address, not the email address of _system_user.

Is this possible?