If you choose ' Never', Mac Mail will leave all deleted emails inside the Trash mailbox until you manually delete them yourself (from there).Then, Mac Mail includes a ' Erase deleted messages when' dropdown menu, which lets you control how soon Mail will automatically purge the Trash from any messages it contains (and remember, this setting is applied on an email account by email account basis, not for the entire email application).If you uncheck this checkbox, any email message you delete (not just from the Junk mailbox) will no longer go through the Trash folder in other words, they will right away be permanently deleted. The ' Move deleted messages to a separate folder' checkbox is checked by default, and we recommend that you keep this setting enabled.