You can remove attachments from messages you're composing as well as from messages you've received. You can only remove attachments from a single message at a time.
1. Click the attachment, and select Remove Attachment.
Delete an attachment from sent or received email message
1. Select the drop-down arrow next to the attachment name and then select Remove attachment. You can also select Upload or Save As first to transfer the attachment to OneDrive or to your computer, then select Remove attachment.
2. Close the message and save changes.
Remove an attachment from the message body
1. To remove an attachment displayed in the message body, double-click the message to open it in a new window.
2. From the Move group in the ribbon, select Actions > Edit message.
3. Click to select the attachment in the message body and then press the Delete key on the keyboard.
4. Close the message and save changes.