Gmail is taking up 1/2 my hard drive

Duh! (me). The trash may be hidden. What you see listed for a Google account is what you allow to show or hide.

Go to gmail.com and login to your email account. Click on the settings gear towards the top right and choose See All Settings. Click on the Labels tab. Of the various labels you can control, for the Trash, make sure the show button is selected, and the Show in IMAP box is checked.

Save the changes, then quit Mail and relaunch it. The trash should then appear.

If it doesn't, your Gmail account may be in limbo mode.

Go back into the settings online and click the Forwarding and POP/IMAP tab. If you've never looked here, the default is that nothing is properly selected. That is, neither the POP nor IMAP radio button is set to Enabled. What happens then is Gmail tries to behave as both and every email gets downloaded to every device you access your mail from, despite appearing to be working as an IMAP account.

Click the radio button to Enable IMAP and save the changes. Once again quit Mail and relaunch it.

This may, or may not purge the pile of data on your drive, but all you can do is try and see what happens.

Oh! Sorry. The left column of the a Finder window looks nearly identical to Mail's left column. Though the Tags and other entries further down from the top should have been a huge clue.

I dug deeper into my own system. The Mail folder in my account is 47 MB. Of which this subfolder…

/Users/xxxxxxx/Library/Mail/V10/MailData/RemoteContentURLCache/fsCachedData

…takes up 22.8 MB of that. I have no idea what that data is. If you try to look at any of them in TextEdit or BBEdit, you see it's binary data, which displays as a lot of gobbledygook.

I might play with that to see what it is. But otherwise, I can't explain the huge amount of space your mail data is taking up.

Okay, that fsCachedData folder is safe to empty. What that's for is any images in your emails. Each time you click on any email that had small images in it (like an Amazon order), an entry gets added back to that folder.

I click on every single email in Mail to see how big it would get. With image data downloaded for all existing emails, the folder is now only 3.3 MB. Down from 22.8 MB.

So, that may be where a lot of your data is sitting. In old, no longer needed or used cached image data.

Well, that's not overly surprising since they're only tiny images used in email body copy. But still, that's 80 MB freed up for the moment.

Other than that, I can only make guesses about the known location of this huge trove of data. Such as, do you know if there are a lot of attachments in your various emails? Mainly, large still images or video files?

Have you ever emptied the trash of emails you deleted? And in that vein, why is there no Trash folder showing in the left column?