I'm currently using Thunderbird with this plugin:

https://github.com/Ericsson/exchangecalendar

It's not perfect, but it's the best solution I've found so far after trying other options such as DavMail, which was far buggier and used more system resources. It's also open-source and actively developed.

Here's a snippet of the features it supports:

• Support Exchange server 2007, 2010 and 2013 (Office365).
• Sync Calendar, Task/Todo and Contact items from an EWS (Exchange) server.
• Create, modify and delete calendar events and task/todo items. They will get synced immediately with the EWS server.
• You can access any Calendar, Task or Contacts folder on your EWS server as long as you have the right primarySMTP or alias email address and enough permissions for the used user.
• Manage “Out of Office”settings for each calendar mailbox.

http://www.1st-setup.nl/wordpress/?page_id=133

I'm currently using Thunderbird with this plugin:

https://github.com/ExchangeCalendar/exchangecalendar

It's not perfect, but it's the best solution I've found so far after trying other options such as DavMail, which was far buggier and used more system resources. It's also open-source and actively developed.

Here's a snippet of the features it supports:

• Support Exchange server 2007, 2010 and 2013 (Office365).
• Sync Calendar, Task/Todo and Contact items from an EWS (Exchange) server.
• Create, modify and delete calendar events and task/todo items. They will get synced immediately with the EWS server.
• You can access any Calendar, Task or Contacts folder on your EWS server as long as you have the right primarySMTP or alias email address and enough permissions for the used user.
• Manage “Out of Office”settings for each calendar mailbox.

http://www.1st-setup.nl/wordpress/?page_id=133