Mac OS 10.11.6, MacBook Pro. I just installed Thunderbird as my default mail app, changing from the Apple Mail application. I have a few issues: 1. I can't set up an incoming mail sound. It is grayed out in Preferences/General. I followed the Help article but it does not apply/work. 2. Messages in my Inbox disappear after I read them. They are going to the Trash folder or the Archive folder. Some are gone all together. I want to keep them all in the Inbox until I decide to move them. How do I do that? 3. In my Apple Mail app I have a few dozen sub folders (mail boxes). Thunderbird did not import them and their messages. I followed the Thunderbird Help article about it, but it did not work. 4. When composing an email message it is double spacing netween paragraphs. I would like to single space instead. Is there a way to set that up? Thanks. Christian.