Mail preview showing the same preview for different messages

Hello Stu-art,

It sounds like you may have isolated the issue further trying to remove the Mail app's saved state by relaunching it while holding down the Shift key. Which tells us the issue is not caused by the saved state.

To isolate it further, does this same issue occur when you view them in safe mode? Learn how below: How to use safe mode on your Mac - Apple Support (Note: Booting to safe mode is slower than expected. Some process and apps may not work here.)

How to use safe mode on your Mac

Safe mode can help you to determine whether an issue is caused by software that loads as your Mac starts up.

Safe mode prevents your Mac from loading certain software as it starts up, including login items, system extensions not required by macOS, and fonts not installed by macOS. It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed.

Safe mode is particularly useful when you're trying to resolve an issue that doesn't seem to be associated with using any particular app. As always, keeping your software up to date is the first step toward resolving any software issue.

How to use safe mode

Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

Apple silicon

1. Shut down your Mac.

2. Turn on your Mac and continue to press and hold the power button until you see the startup options window.

3. Select your startup disk, then press and hold the Shift key while clicking “Continue in Safe Mode.”

4. Log in to your Mac. You might be asked to log in again.

Intel processor

1. Turn on or restart your Mac, then immediately press and hold the Shift key as your Mac starts up.

2. Release the key when you see the login window, then log in to your Mac. 

3. You might be asked to log in again. On either the first or second login window, you should see ”Safe Boot” in the upper-right corner of the window.

If the issue continues in safe mode

If the issue continues while in safe mode, or your Mac restarts several times and then shuts down while starting up in safe mode, you should reinstall macOS and make sure that your Apple software and third-party apps are up to date.

If the issue doesn't continue in safe mode

If the issue doesn't continue while in safe mode, leave safe mode by restarting your Mac normally. Then test for the issue again. The issue might be resolved.

If the issue returns after leaving safe mode, startup items are probably at fault. Apps can install such items in numerous places, and they aren't always easy to find or recognize. For that reason, you should first make sure that you've installed any available updates for your Apple software and third-party apps.

If updating your software doesn't help, try any of these solutions:

- Test your login items.

- To learn whether software in your user account is causing the issue, set up a new user account, then log in to it and try to reproduce the issue in that account.

- Unplug all accessories from your Mac, including printers, drives, USB hubs, and other nonessential devices. You could have an issue with one or more of those devices or their cables.

- Reinstall macOS.

If you still need help, please contact Apple Support.

Learn more

Some features might not work in safe mode, such as movie playback in DVD Player, video capture, file sharing, Wi-Fi, some accessibility features, some audio devices, and some devices that connect via USB, Thunderbolt, or FireWire. Accelerated graphics are disabled, which could cause blinking or distortion onscreen during startup.

Use sections, 'If the issue continues in safe mode' and 'If the issue doesn't continue in safe mode', depending on your results there to solve the issue.

If it continues to occur, does this only happen with specific emails or all emails you attempt to preview?

Hoping to hear how it goes, cheers.

We’ll be here for you, Stu-art. We look forward to learning the results.

All the best.