From Debian bug #917993:
From: Nye Liu <nyet@nyet.org>
Subject: wmbiff: gmail (and many other IMAP servers) now require SNI
Date: Tue, 01 Jan 2019 18:33:51 -0800
wmbiff/gmail imap4: Need new connection to ***@gmail.com@imap.gmail.com
wmbiff/gmail comm: certificate passed time check.
wmbiff/gmail comm: server's certificate (OU=No SNI provided\; please fix your client.,CN=invalid2.invalid) does not match its hostname (imap.gmail.com).
wmbiff/gmail comm: server's certificate does not match its hostname.
wmbiff/gmail comm: to ignore this error, run wmbiff with the -skip-certificate-check option
Signed-off-by: Jeremy Sowden <jeremy@azazel.net>