I have read in the TOS for the Matrix server that all messages are deleted after one year. If I am talking with someone, does that mean that messages that are older than a year are deleted on my side, or both sides of the conversation? What if the chat is E2EE? If I am using a device that is signed in and has seen old messages, are they removed from that device too?
That’s not how Matrix works. Matrix runs an internal DAG that stores all messages basically permanently.