POP3S (Post Office Protocol 3 Secure) is a secure message collecting protocol. POP3 is usually the default protocol for email clients and is ideal for users who access their PSMailbox from a single computer and have a very reliable internet connection. Messages are automatically collected from the PSMailbox to the local email client where they can be stored, replied to, etc. Generally, once a message has been collected by the client, it is deleted from the PSMailbox automatically, although settings may vary.