If the path to a far away BBS requires a few nodes to be traversed, then many days can accumulate between you sending a message, and a far away place getting it. Similarly, if someone were to reply to that message, that same time delay would apply to the return path. As a result, it is not uncommon to see a 'mail turnaround time' of a week or more in Echomail areas - the time between you sending a message to someone, until you get a reply from that person. So what usually happens is that you have several conversations going on at once, to many people, and even to the SAME person. This can and does get confusing, but as long as you realise the delay is present in ALL your correspondence, much heartache can be avoided.
Messages are public, unless stated otherwise.
So, you enter a message into an Echomail area, and every other BBS that shares that area, will add your message to its copy of the echo, where a user there may read it, and even reply to it. You need two pieces of information to send a message via netmail. You need to know the user's name. This isn't a street address, it's a unique number assigned to each BBS in the Fidonet network. FIDOnet addresses play an important part in determining where mail goes to.