Dovecot and Self-signed issue

[Michael A. Peters]

I use dovecot on several servers. One of them uses a self-signed cert, 
it's just me.

It worked fine until yesterday when I upgraded my desktop (NOT the 
server) to CentOS 7.4

Now thunderbird complains when it starts up, and won't let me confirm 
the security exception.

On the server the following error occurs in the log:

Sep 25 20:17:49 librelamp dovecot: imap-login: Disconnected (no auth 
attempts in 1 secs): user=<>, 
rip=2600:1010:b064:f260:e83e:562d:2316:18df, 
lip=2600:3c01::f03c:91ff:fee4:310c, TLS handshaking: SSL_accept() 
failed: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown 
ca: SSL alert number 48, session=<u7agQAlasK8mABAQsGTyYOg+Vi0jFhjf>

I believe this is a client issue, as it worked just fine in CentOS 7.3 
client, but I am hoping this has been seen and fixed before.