EML is a file type that email get sent in. This is also known as Plain Text.
You can not turn it off as such but you can select and use Rich Text.
You need to log onto your email account using a web browser then go to the settings which is found by clicking on your user name on the top right hand side then click Mail in the left hand column and on the page that opens scroll down until you see the "Compose Messages in Rich Text Format". If it is not ticked you need to tick it and then click "Save"
