You can choose the default behavior for opening all Office
documents in Matter365 and actions that will happen while you're storing an email in Outlook.
To do that, go to Matter365 app settings and select Document and Email settings.
Matter365 application settings
You can select either Web client or Desktop client as your default option for opening documents, and for "Store email" functionality, you can choose to save .eml file in OneDrive, or just forward the email to the group inbox of the Matter you select.
Settings you can choose regarding default application client and store email behavior
If you’re using Web client, make sure you allow pop-ups in your browser, since documents will always open in a new tab of your browser.
Example of blocked pop-ups in Google Chrome, and selecting an option to allow them:
Enabling pop-ups, in case they are disabled by default in your browser