Hi ae71386ae,
I think they mean that you should use the work email for your recommender, not for yourself. That way the recommendation seems more credible, as if written by your actual recommender (who also has to mention where he works, so the name of the company should match the email address/domain).
Are you worried about asking someone else at your work place for a recommendation because your boss may find out? well, in that case I would suggest either finding another recommender (and explaining to the school why you can't provide a recommendation from your current job) or using the private email address (and again - explaining that to the school to make sure the recommendation from the gmail/hotmail/yahoo account is accepted).
To read more about the recommendation process and selecting your recommenders, please visit:
https://www.aringo.com/MBA_Recommendations_Process.htmGood luck!