IMAP TLS after upgrade from 3.1.17 to 3.2.3

hello dbmail

i just upgraded dbmail from 3.1.17 to most recent stable 3.2.3

with the old version 3.1.17 i could do an IMAP account setup in 
thunderbird with SSL/TLS on port 993

with the new version 3.2.3 thunderbird now throws me an error that this 
connection type is not supported by the IMAP server.
if i then switch to STARTTLS on port 143 all is working fine.

before i start into debugging this on my server ...

is this the expected behavior with the IMAP TLS setup in 3.2.3?
is SSL/TLS on port 993 not supported?
is STARTTLS on port 143 the only supported encryption?

if not ... how can i best debug this issue? what do i need to do to make 
SSL/TLS on port 993 work again?

i'm runnning an opensuse box leap 42.1 with all the latest patches 
installed ...

thanks to the dbmail devs for providing such a nice software over all 
those year ;)

greetings
becki