Trash

If it's sitting in your Trash, yes, mail is automatically deleted at an occasional interval. You can also completely delete it yourself, by clicking "Empty" beside your Trash.

After messages are emptied from Trash, they're permanently deleted from the Yahoo! Mail server and can't be recovered.

Bulk

You can choose how long you want to keep messages in your Bulk folder. You can choose to immediately delete upon receipt or keep messages for one week, two weeks, or one month. The default setting is one month.

To edit this feature:

1. Click "Options."
2. Click "Spam Protection."
3. Click the "Save these messages in the Spam Folder for" button.
4. Choose a desired timeframe from the pull-down menu.
5. Click "Save Changes."

Other Folders

Mail in your Inbox and in all your other folders stays in your account as long as you want it to!