The University currently allows email submission to mail.ru.ac.za on port 25 when users are on its campus. Such connections are not secure, and have been informally deprecated for some time. In addition, they are now widely used by viruses and other malware as a means of replication. Support for this service was retained to reduce the disruption for people with older mail clients, and the intent was that over time natural attrition would remove the need for this.
Unfortunately, largely as a result of poor default settings in popular email clients, we continue to see new email clients configured to use unsecured and unauthenticated connections to the mail submission servers. For this reason, we will be discontinuing support for unauthenticated submission using port 25 at the end of June 2015.
You do not need to do anything about this immediately; if your computer is scheduled to be upgraded or replaced at the beginning of 2015, that would be an appropriate time to make this change. However, from July next year, any email client that does not make use of authenticated, encrypted submission will not be able to send mail.
If you'd like to check your mail settings, information on correctly configuring most mail clients can be found at http://www.ru.ac.za/static/it/configs/. There are also generic instructions showing the correct settings for any client.