Some attachments—like images or one-page PDF documents—are displayed directly in the message. If you’d rather view the attachment as an icon, Control-click it, then choose View as Icon from the shortcut menu. To display the attachment again, Control-click it, then choose View in Place.
In the Mail app on your Mac, select a message that includes one or more attachments.
Choose Message > Remove Attachments.
The message remains in the Account Information preferences in Mail.
If you send or forward images or PDF documents you receive to other people, you can add comments, drawings, or a signature to the attachments before you send them. See Delete emails in Mail on Mac