This is a common issue and is often due to a display or encoding problem. Here are a few things you can try to fix it and see the email's content:
1. Check the Display Settings
Sometimes the message body is there, but it's being displayed in a very small font, or perhaps in a color that blends with the background.
- View > Message > Plain Text Alternative: Go to the View menu at the top of your screen, hover over Message, and click Plain Text Alternative. If the email was sent as HTML, this will strip out the formatting and might reveal the text.
- Zoom In: Try zooming in on the message. In the Mail viewer, you can often do this with Command plus "+"
The fastest way to confirm if the content is truly missing is to view the email outside of the Apple Mail application.
- Webmail: Log in to your email provider's website (e.g., Gmail, Outlook, Yahoo) and view the message there. If the content appears in the web browser, the issue is definitely with your Apple Mail app.
- Rebuild the Mailbox
If the issue is isolated to the Mail app on your Mac, rebuilding the mailbox can often resolve display glitches. This process essentially deletes the locally stored index and downloads a fresh copy from the server.
- Select the mailbox (e.g., your Inbox) that contains the problematic email.
- Go to the Mailbox menu at the top of your screen.
- Select Rebuild.