A Fedora Linux-based mail server administrators noticed issues with the Microsoft Outlook mail client after updating the distribution. Diagnosis of the problem showed that in the new version of the Dovecot 2.4.3 IMAP/POP3 server package, authentication via IMAP and POP3 protocols with the password transmitted in plain text was disabled by default.
Outlook users had the option enabled to connect to the mail server using encryption, but the mail client continued to use network port 110 for POP3 instead of switching to port 995, which is used for TLS sessions to the POP3 server, and did not utilize the STARTTLS extension to switch to a TLS session. Some older Outlook configurations, without any warning, ignored the flag to enable TLS encryption when explicitly using port 110, sending USER and PASS commands in plain text immediately. The earliest release of Microsoft Outlook in which the issue was noted dates back to 2007.
Forrás: opennet.ru
