Outlook -- Opening an Email in a Separate Window in Online Outlook
Recommended Option:
There is a simple way to open an email in a separate window when using the online version of Outlook for Office 365 that you use in an internet browser.
Double-click the email in the "Inbox" panel. That's it.
Double-clicking the email in the "Inbox" panel will make that email open in a new window in your internet browser.
If you are in a different folder than your "Inbox," you'll double-click the email in the same panel. But the panel will show the name of the folder.
Double-clicking the email in the panel showing emails in whatever email folder you are viewing will make that email open in a new window in your internet browser.
There are at least two other methods, however, as well, described below.
Alternate Option 1 -- If Already Replying in Left Reading Pane:
If you are already replying to an email in the far-right "Reading Panel," click the double arrows icon in the "To" row of the message.
Then click the overlapping squares icon, or pop-out icon, in the upper right.
Alternate Option 2 -- Before Replying in Left Reading Pane:
You can also click the tiny down arrow or next to "Reply All" or "Reply" in the right Reading Pane.
Then click "Open in a separate window."