As noted previously, we've been planning on enforcing SSL/TLS encryption of all communication between a user’s email software and our servers, ensuring that no one can eaves drop on your username or password to steal your login credentials.
Over the past month and a half we've been sending notification emails to all users using insecure connections with details of how to fix their email software configuration. During that time the vast majority of users have already reconfigured their email software to correctly use secure and encrypted connections.
At some point we have to completely disable the insecure connection ports and we've decided to do that on July 14. From July 14 onwards, only the official configurations described on our Server Names and Ports help page will be active and supported, all other ports and hostnames will be disabled.
The vast majority of users are already using the correct configuration and won't be affected. Only the small number of users still using insecure configurations (despite the regular notifications we've been sending them for the last month and a half) will have problems. We're now contacting those users to let them know they have only 5 days left to change their configuration.