Please refer - https://docs.zivver.com/en/user/officeplugin/references/release-notes.html

6.4.0$$$FixtENG-9285 - Opening an EML file in Outlook will save the message in the Inbox folder.t$$$FixtENG-9669 - The Zivver Office Plugin may fire an exception “Object reference not set to an instance of an object”.t$$$FixtENG-9844 - It is impossible to send a Zivver message if the file name of an attachment contains brackets.t$$$FixtENG-10066 - The Zivver Office Plugin does not resolve distribution lists to their individual members.t$$$FixtENG-10425 - When using v6.1.x / v6.2.x of the Zivver Office Plugin; closing Outlook may take longer than when using earlier versions of the Zivver Office Plugin.t$$$FixtENG-10460 - Users may intermittently become stuck on the “checking message” screen in the Zivver Office Plugin after sending a message.t$$$FixtENG-10489 - When a read only MSG file is closed; you are prompted to save your changes.t$$$FixtENG-10958 - The Zivver Office Plugin may fire an exception “COM object that has been separated from its underlying RCW cannot be used”.t$$$FixtENG-11099 - Outlook may crash upon startup.t$$$FixtENG-11158 - The Zivver bar may overlap part of the window when replying or forwarding in inline mode.t$$$FixtENG-11518 - Working with calendar items may be slower when the Zivver Office Plugin is enabled in Outlook.t$$$FixtENG-11812 - After restarting Outlook the Zivver message view is missing for sent Zivver messages.t$$$FixtENG-11980 - Forwarding may not work when the Zivver Office Plugin is enabled.t$$$FixtENG-12106 - The reply and forward buttons do not work for folders that have been made available through folder permissions rather than through mailbox permissions.t$$$FixtENG-12343 - The intResource.dll file may be flagged by Windows Defender.