Thanks, Edward,

I've got the right boxes marked, but those folders don't show up. See screenshots.

Well, you were right, but the Sent folder there was just one I created, thinking that if I made one and labeled it Sent, it would appear in the right place and look like the ones up above. So the Sent folder there is just that and not a true Tbird one; I'll delete it. Also, where is the Drafts folder? And I'm also missing Drafts under the account just above this one. And in the setup for these accounts, all the right folder options are checked. I know I must be doing something wrong, but can't figure it out.

Okay, Edward,

I figured this out. Those folders don't appear until you actually use them. Evidently I'd done some Tbird testing with a previous version, but uninstalled it a while back, and then when I reinstalled and updated, I didn't 'exercise' the accounts sufficiently. Sure enough, as soon as I created an e-mail and sent it, I got a Sent box for that account. And I can delete what is in the box, and the box remains. Same with the Drafts folders. Dump out of composing an e-mail, but tell Tbird to save it in 'Drafts,' and, voila, the folder appears. Again, empty it and the folder remains. I think I'm good to go now, but thanks very much for sticking with me on this. I probably would have given up and not looked deeper if I'd been entirely on my own.