Is it permissible to speak to and greet the husband's brother while veiled?

A woman is permitted to speak with her husband's brother provided that she adheres to proper etiquette in speech, and that the conversation is appropriate, without any softness in speech that would make it alluring. It is permissible to greet him if there is no fear of temptation (fitna). However, shaking hands with him is forbidden by the unanimous agreement of the four Imams.