Rackspace is updating it's security measures and it may require your action. They are removing insecure (Standard) access for IMAP,  POP, and SMTP. This is necessary for migration to Open-Xchange, and your email accounts will be more secure.

Insecure access sends the username and password in plain text over the network. Bad actors can exploit this vulnerability to steal the username and password for the mailbox. Secure access encrypts the data, protecting against main-in-the-middle attacks, attackers reading a message in transit, and messages being forwarded to attackers.

To prepare for this change, you'll need to reconfigure any mailboxes connecting insecurely.

Reconfiguring mailboxes before insecure access is removed will ensure continued email access without disruption.  The removal of insecure (Standard) access has started and will be complete by December 2022.