It is also possible for you to use the searcher there. This makes everything so much easier and the kids can learn how to search in the process. Our next advice is that you leave the list and write privately when the exchange is established. The list is a thin shell of protection that we have created against adults that wants to contact children. Some teachers don't feel they need this protection but for those who feel the need they can easily leave the list and write privately when they feel comfortable with the exchange.
Individual exchange is after all easier between private addresses.
But if you want to send to the list it's easy. It is a lot of work to organise the exchange for a whole class. Please consider to participate as a class. Try to find a partner class to carry out the exchange with. Make a plan for the exchange so that class knows when they can relay on an answer and have something to look forward to.