Using File, Print... or Ctrl+P within the browser may cause some HP printers to lock up when printing from Internet Explorer.
It is recommended to use the three dots (...) above the message to select Print rather than using File, Print on a browser.
This will open the message in a new window and launch the browser's print dialog. You can print like normal from there which should prevent printer problems and save paper by focusing on the content of your message.
This method has proven to be the most compatible way to print emails from PantherMail powered by Office 365.