I sent an email to myself and 'saved' it. There is no indication of where it went or where it is now. I saw elsewhere to open "My Files" folder. There was a "My Files" folder on all my previous S phones, but not this one. Trying to navigate the S9 is a major bummer. There seems to be no option to Move any files to a preferred folder or area.
Normally the save option uses the download manager to save the attachment to the download folder in internal storage. It usually leaves a notification in the notification panel.
If you add an image attachment to the email and save it you should be able to see the downloaded image in the gallery app as an album titled downloads.
To find the My Files App check the One Ui Homa settings menu, scroll down to hide apps and if My Files has a check mark next to it remove it.
Open system settings, apps and search or scroll down to My Files. Open it and scroll down to the bottom and select app details in store. It should open play store and have a button that says open.
If it's not listed open the galaxy store app or the play store app and search for Samsung my files and install it.
You should be able to long press on an empty spot on the home screen. When the new menu opens on the bottom right side tap home screen settings. It should take you straight to the settings menu.