Log in to your Outlook on the Web account and go to the Mail app


The main view of all apps in Office 365































Then, go to the gear icon at the top right-corner and click Mail


Go to the Option section in Outlook on the Web.














































On the left pane, extend the Mail section, then Layout and select Email signature


Go to the Email signature section in Outlook on the Web.














































Please note you can't copy and paste images into this area,


You need to manually upload them using the image icon in the text editor