Outlook 2016 still allows you to edit the subject line of incoming messages. It’s just a little different to access than previous versions of Office.
How to edit a message’s subject line in Outlook 2016
Open the message by double-clicking its entry in the message list. Editing the subject from the reading pane does not work.
With the message open in its own window, expand the header fully by clicking the caret in the bottom right corner of the header (the top section of the email where the To, From, Subject, and Date are located).
Click on the subject and start typing. You can delete or add to the subject line just by editing it to what you want it to be.
When you are satisfied with the new subject, you may close the message. You will receive the message:
The properties of the message “[new subject]” have been changed. Want to save your changes to this message?
Choose ‘Yes’ to save the changes and your message will now have the new subject text.
Why might you want to edit the subject line?
People have different email organization methods and some people have different email habits. If somebody replies to a previous message but changes the topic, you might want to update the subject line so that you can find it in the future. Some people also use very generic subject lines – they email IT with ‘computer problems’ but that IT Pro gets dozens of emails a week of ‘computer problems’.
It’s a small detail but good to see that Microsoft is still offering the edit subject in the latest version of Outlook. You can edit the rest of the message by opening the message and going to the Message tab on the Ribbon, Action, and then Edit Message. Make your changes (such as adding an attachment or changing the body) and click the save button.