Administrators of mail servers based on Fedora Linux have recently brought attention to issues arising in the operation of the popular mail client Microsoft Outlook after a distribution update. The problem was diagnosed to be stemming from the new version of the Dovecot 2.4.3 IMAP/POP3 server package, which by default, disallowed authentication through the IMAP and POP3 protocols with the sending of passwords in plain text during sessions without encryption.
Despite Outlook users having the encryption option enabled to connect to the mail server, the client continued to use the network port 110 for POP3 instead of switching to port 995, which is designated for TLS sessions to the POP3 server. As a result, certain older configurations of Outlook were simply ignoring the TLS encryption flag if port 110 was explicitly specified for cleartext communications. This issue was traced back to Microsoft Outlook versions as far as 2007.