We used to relay messages in a mailbox once per day and got all new ones (called "Maustausch" https://de.m.wikipedia.org/wiki/MausNet https://de.m.wikipedia.org

We used to relay messages in a mailbox once per day and got all new ones (called "Maustausch" https://de.m.wikipedia.org/wiki/MausNet https://de.m.wikipedia.org/wiki/MausNet). It was pretty cheap because all group and personal messages came in one compressed batch and you had stuff to read and respond for a day. The BBSes exchanged all messages in a tree call hierarchy, you could reach everybody within that one day hop.