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

imap: exchange.uibk.ac.at
username: c703xxxx
port: 993 	 
encryption: SSL/TLS
Authentication method: Normal Password

smtp: smtp.uibk.ac.at
username: c703xxxx
port: 465 	 
encryption: SSL/TLS
Authentication method: Normal Password

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): Installation und Konfiguration von Mozilla Thunderbird

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 v3.9.0

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. doku