With the current Thunderbird I can not connect to one of my IMAP servers that uses a self-signed cert. Virtually identical IMAP servers that use CA signed certs work I was a bit out of date when I updated to 7.4 and was running Thunderbird 45.6.x and it worked. When I connected from evolution (which I do not like) it worked. When I connected with my laptop still running 45.6.x it works. so - I rebuilt thunderbird 45.8.0 from 7.3 updates (newest that isn't 5x.x.x series) and did an --oldpackage update with RPM and it works again. When rebuilding the old thunderbird in mock I had to add the following: BuildRequires: dbus-glib-devel Either the build system used by CentOS automatically includes that, or a build dependency use to pull that it but no longer does. Anyway if anyone is having a similar problem, that's a solution. -=- This is what I see in the mail server log when current CentOS thunderbird tries to connect: 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> --- Since it works with current evolution and with older thunderbird, I assume it is a bug in current thunderbird when the server is using a self-signed cert. Don't know if same thing happens on pop. I use IMAP on 143 using starttls