If you use Apple Mail on OS X, then you know that when you empty the trash, it normally purges all the deleted messages for all your accounts. If you only want to purge deleted messages from one account, however, there is another way.
Emptying the trash with Apple Mail is accomplished by right-clicking on the Trash icon in Mail and then selecting “Erase Deleted Items” from the resulting context menu.
That seems pretty simple and straightforward. You’re then presented with a dialog that asks you if you want to delete the items in the selected mailboxes. “Selected” means all the mailboxes.
If you select a specific trash for an individual mailbox, then you’re shown the exact same dialog. Again, it will delete the trash from all your mailboxes, not just the one you think you’re emptying.
Okay, so there may be a point at which you don’t want to necessarily purge your deleted items just yet. Perhaps you’d prefer to clean out your mailboxes but hang onto things just a bit longer. It’s not unheard of, though perhaps a little unorthodox and risky, but it does happen.
Nevertheless, you may also still want to empty your other trash folders, leaving one or two intact. It’s actually possible to do this using the “Mailbox” menu. Click there and then choose “Erase Deleted Items” and select the individual mailbox you want to purge.
Notice now that the dialog changes to reflect the specific trash mailbox we’re purging.
If you have others that you want to clear out while leaving one or two untouched, you can simply use the Mailbox menu to do this.
Again, while it may seem counterintuitive to want to hang onto deleted messages, there are any number of reasons why some people may want to be cautious about it. For example, if you set up a rule intended to weed out certain types of messages, but want to make sure it didn’t catch anything you want to keep.
It’s always a good idea to err on the side of caution, especially if you access your work mail from home. Anything can happen so making sure you choose when and how you empty your deleted messages can really help you avoid disaster.