The best way is to use a forum where "everyone is subscribed"
(this is visible at the top of that page as you can see below), and then post a message there.
If you want to send a personal mail, click on the photo of the person who wrote the posting you want to refer to. Then the personal email-address of this person appears and you can send him or her a personal email.
When “Intercultural Journey” is written in the reference line of a mail, this is a posting to a forum which is sent out to all subscribed persons. Usually, it is up to you if you want to comment. If the message is a task from a moderator and you have to answer, the message will explicitly say so. It is up to you to answer or not except if it is a task.