After migration from Ubuntu 12.04 to Ubuntu 14.04 and upgrading afterwards ZCS 8.0.9 to 8.8.6, I have weird issues with POP3 clients.
Also SSL was upgraded from commercial SHA-2 with SHA-1 root to full SHA-2 with SHA-2 root.
Now, among 2000+ users, I can see some dozens of POP3S connections on port 995, and inside Zimbra Admin I see dozens of POP3S success authentications.
BUT some others, maybe a dozen of them, simply cannot authenticate against POP3S on port 995. They are using Windows 7 with Outlook 2013 or 2016.
SMTP authentication is also required, and they can send using SMTP over 465 or 587 ports, no problem.
Only POP3S is problematic on *SOME* computers.
In nginx log I see:
Code: Select all
[info] 16250#0: *99998 upstream sent invalid response: "-ERR LOGIN failed" while reading response from upstream, client: <client IP>:28801, server: 0.0.0.0:995, login: "<user@domain> ", upstream: 10.10.11.50:7110 (<client IP>:28801->10.10.11.50:995) <=> (10.10.11.50:34574->10.10.11.50:7110)