Faced with such a problem:
After upgrading zcs 7.2 to 8.0 with kerberos authentication thunderbird started ask me: "Ticket Kerberos / GSSAPI was not accepted POP3-server. Please check that you've entered the Kerberos / GSSAPI realm. Mail server «mx.local» replied: Line is too long: 2002".
The logs of tunderbird shows that the problem is in the server, after the transfer of the longest line. In zcs 7.2, everything works fine with the same "long kerberos" string.
After clear installation zcs 8.0 on ubuntu 12.04 the problem not resolved.
Please help solve the problem.