To manage growth efficiently on BetterMost, please delete private messages you no longer need to keep in your boxes. There is no limit on the number of messages you can send and receive, but it can be easy to pile up a huge number of them if you forget to clean them out from time to time. There is no issue with this right now, but I like to encourage good housekeeping practices here.
If you want to keep a copy of the message you are sending, you need to check the box that saves a copy of your message in your outbox. Remember to clean those out when you no longer need them as well.