My mother-in-law is a frum trained massage therapist - who applies massage to women only. My question: under what conditions is it halachically permissible for a married woman to give a man (not her husband) a massage?

A man physician can treat a woman and vice versa, the reason is since they are professionals there are no immodest aspects involved. [Yet here also the recommendation it to find the good male doctor for men and same for women] I have discussed this issue with some Poskim and these are the conclusions, and so, if the massage treatment is therapeutic it should follow the same ruling above. However since massage more than other medical treatments may have a sexual undertone to it is therefore highly recommended for men to be treated by men and women by a woman. In case this would lead to a great loss of money, and similarly in case the massage is only on arms or legs and not body, a more lenient approach can be taken. If the massage is for relaxation and not for medical treatment there is no place for any leniency.