mailaddress: firstname.lastname@uibk.ac.at
username: c703xxxx

imap: exchange.uibk.ac.at
port: 993 	 
encryption: SSL/TLS

smtp: smtp.uibk.ac.at 	 
port: 465 	 
encryption: SSL/TLS

Account Settings → Composition and Adressing → edit Directories:

General Settings:

Name: Uni Innsbruck
Hostname: ldap.uibk.ac.at
Base DN: o=Universitaet Innsbruck,c=AT
Port: 389
Bind DN: empty
use secure connection (SSL): not activated

https://exchange.uibk.ac.at

see ZID config page (in german): http://www.uibk.ac.at/zid/software/pc/mailprogramme/thunderbird_v3/

Official support is not given, neither by Mozilla nor Microsoft.
Nevertheless, there is an (almost) stable project which is offering calendar support for Thunderbird over a xpi-PlugIn:

Exchange EWS Provider v3.5.0 stable / v3.6.0 Beta1

Stable for reading Exchange Calendar entries. It is also possible to add/update entries, but it seems like it takes some time that all data is synchronized properly.