Evolution is reporting that our IMAP server has an expired cert. It doesn't; it's just that for some reason glib-networking has reimplemented a bunch of security-sensitive code instead of just using GnuTLS as it should. And has got it wrong. Full details in upstream bug.
*** Bug 1286034 has been marked as a duplicate of this bug. ***
(Since we're not currently aware of any security issues in this code affecting current releases, I don't think we need to backport anything here.)