Package: libnss3 Followup-For: Bug #787505 I was bitten by this also. My imapd server was a rather dull courier-imap-ssl server, and the DH key length was left as is since its installation (probably etch). My config file was mostly untouched, and no warning came.
I followed the procedure here : http://apple.stackexchange.com/questions/206448/imap-account-stopped-working-after-upgrade-to-ios-9-problem-with-cacert-certif?answertab=active#tab-top and it worked fine. -- System Information: Debian Release: 8.2 APT prefers stable APT policy: (950, 'stable'), (200, 'unstable'), (80, 'experimental') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 3.16.0-4-amd64 (SMP w/2 CPU cores) Locale: LANG=fr_FR.utf8, LC_CTYPE=fr_FR.utf8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/bash Init: systemd (via /run/systemd/system)