Can't connect to Kolab/Guam 16 with Thunderbird 45.7

[Gufler, Thomas]

Hello,

having a interesting problem. I can connect with Thunderbird on Ubuntu 
16.04 to a Kolab server (roundcube works as well) but not with 
Thunderbird on Arch or Fedora 25 (to the same system).
Trying to create an Thunderbird Account on this two systems ends with an 
error "Configuration could not be verified - is the username or password 
wrong?".

In the guam error.log I get:

error] <0.89.0> Supervisor {<0.89.0>,kolab_guam_listener} had child 
session started with {kolab_guam_session,start_link,undefined} at 
<0.174.0> exit with reason 
{{function_clause,[{ssl_cipher,hash_algorithm,"\b",[{file,"ssl_cipher.erl"},{line,1196}]},{ssl_handshake,'-dec_hello_extensions/2-lc$^0/1-1-',1,[{file,"ssl_handshake.erl"},{line,1706}]},{ssl_handshake,'-dec_hello_extensions/2-lc$^0/1-1-',1,[{file,"ssl_handshake.erl"},{line,1707}]},{ssl_handshake,dec_hello_extensions,2,[{file,"ssl_handshake.erl"},{line,1706}]},{tls_handshake,decode_handshake,3,[{file,"tls_handshake.erl"},{line,184}]},{tls_handshake,get_tls_handshake_aux,3,[{file,"tls_handsha..."},...]},...]},...} 
in context child_terminated


I already tried to switch from the certificates in the standard 
installation to letsencrypt signed one - but with the same result.

Any ideas?

Best regards,
Thomas