Every message you read adds to the Mail app’s cache.
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To clear the Mac Mail app’s cache, you’ll need to use the Finder to find the app’s internal data.
Once you locate the Mail app’s data with the Finder, you can just delete it.
Clearing the Mac Mail app’s cache will force the app to redownload all your messages.
Like most apps, the Mail app on your Mac has a cache. It uses this cache to save emails you’ve read recently, so it can load those emails faster the next time you need them.
But if you use the Mail app a lot, or have the app synced with a lot of different email accounts, that cache might balloon in size. When that happens, the Mail app will slow down. Luckily, it doesn’t take much work to reset that cache.
How to clear the Mail app’s cache on your Mac
To clear the Mail app’s cache, you’re going to need to delve into your Mac’s internal files, which are usually kept hidden.
1. Fully close the Mail app.
2. Open up a Finder window and click Go at the top of the screen, and then Go to Folder…
3. In the text box that appears, type ~/Library/Mail and then press the Return key. This will bring you to the folder that your Mail app stores all its data in.
This is the easiest way to reach your Mail folders.
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4. Once there, find the folder that’s named V, followed by a number. In current versions of macOS, this will likely be V8 or V9.
5. Delete this folder by right-clicking it and selecting Move to Trash.
Delete the “V” folder.
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This will delete all the emails that your Mail app has saved in the cache.
The next time you open the Mail app, it’ll redownload your messages from scratch and recreate the “V” folder.