I regularly exchange emails with two remote contractors who are from Indonesia. I will need to send a work related email later today or tomorrow. Should I mention anything about the recent terrorist attack, for example "I hope everything is OK", or would that be inappropriate?
If you want to send condolences, send it in a separate message. First, mentioning it as an aside to some other message could be construed as not giving the event its due. Second, it's usually wise in business correspondence not to commingle issues. For example, if you were to discuss two completely separate business issues with these individuals, you would generally do so in two separate messages, the reason being that the message may require other people's attention and may need to get forwarded on to be seen by other eyes. If that happens, your personal message gets passed around, replied, cc'ed, forwarded, replied again, etc., possibly for weeks or longer, and the tragedy gets reread and relived every time. My advice, stick to the topic at hand and send condolences separately.