Office 365 (Known Issues) - Unable to Open Print Window in Outlook on the Web
Resolution Status: Unresolved. This issue has been acknowledged by Microsoft, and a fix is being rolled out.
Individuals are reporting an inability to open the print window in OotW and are therefore sporadically unable to print in OotW across multiple browsers.
Individuals experiencing this issue should use the appropriate keyboard shortcut (Ctrl + P in Windows computers or command + P on Macs) to initiate the print window from his/her browser. Alternatively, individuals may be able to print using a different web browser.