The prohibition, which is listed in the Mishnah tractate titled Avodah Zarah, allows for benefit to be derived from such milk, while drinking it is forbidden out of fear that a non-kosher animal's milk was mixed into the kosher milk.
According to the Mishnah tractate Avodah Zarah, a prohibition exists regarding this type of milk.  It is permissible to derive benefit from this milk but consuming it is forbidden out of concern that non-kosher milk has been mixed in.