Is it permissible to work in e-marketing for foreign companies involved in forex trading and binary options, given that some of them rely on the client's loss? And is it permissible to offer them some services but not others, or must one refrain from dealing with them entirely?

Trading binary options is impermissible, and therefore, marketing them is also impermissible because it constitutes cooperation in sin and transgression. Currency trading is permissible only if it is free from শরীআ (Islamic law) prohibitions. If it involves a শরীআ prohibition, then it is not permissible, and consequently, marketing it is also impermissible. The fact that companies will turn to other marketers does not permit cooperation in the forbidden. It is only permissible to work with them in services that are lawful according to শরীআ.