Here is a list of issues that were fixed in this release - build 2.6.19.

Issue Key Description
AVSUPPORT-33827 When email custom query report was generated, wherever no subject was presented (a blank subject in the subject column) it was impossible to drill down and investigate the email (not linkable).
AVSUPPORT-26730, AVSUPPORT-26308, AVSUPPORT-25440 Some calendar invites were not being created on the calendar since the invitation was updated in O365. The issue was related to a more generic email connectors issue that caused some modification to emails, and the MTA and connectors are now changed accordingly.