Unlike many email accounts, data mailboxes have an unlimited capacity. As a data mailbox user you will never miss a message just because your mailbox is full. On the other hand, data messages are stored in your mailbox only for 90 days. You can read and save them in that period of time.
If you do not want to worry about storing and archiving of your messages at all, why not use Data Safe. Data Safe automatically archives data messages so that you will never lose any important message.