Design flaw permits storing of incoming emails in the "sent email" storage bins.

1. It's up to the user to move things wherever they'd like
2. This has nothing at all to do with the portable version

It's user preference whether to display just Sender, just Recipient or both columns for each type of folder (just click on the column selector above the scroll bar). Or you can use the Show InOut extension to add a "Correspondent" column that displays the Sender unless one of your Thunderbird identities sent the message, in which case it displays the Recipients instead. Find it here.

Since the original Netscape Mail, I've configured my accounts to Bcc all messages to me and save sent messages to the Trash folder. The Bcc allows me to maintain both ends of a thread (including sent-mail transport headers) in a single folder, automatically filed by Message Filters. In case of a transport problem (where I don't get my Bcc back in a reasonable time), the Trash folder allows me to retrieve the original sent message (sans headers) and doesn't require any additional effort to maintain.

In configuring Show InOut, I placed the new In/Out (icon) column after the Subject, followed by the new Correspondent column. To make it more readable, I added the following to my Data\profile\chrome\userChrome.css:

/* Show InOut */
	treechildren::-moz-tree-cell-text(out) {
	   font-style: italic !important; 
	}

	/* change the icons, be sure to use !important */

	treecol.inoutColumnHeader {
	   list-style-image: url("chrome://messenger/skin/messengercompose/compose-toolbar-small.png") !important;
	   -moz-image-region: rect(32px 16px 48px 0px) !important;
	}
	treechildren::-moz-tree-image(sio_inoutCol, out) {
	   list-style-image: url("chrome://messenger/skin/messengercompose/compose-toolbar-small.png") !important;
	   -moz-image-region: rect(0px 16px 16px 0px) !important;
	}
	treechildren::-moz-tree-image(sio_inoutCol, in) {
	   list-style-image: url("chrome://messenger/skin/icons/readmail.png") !important;
	}
	#threadTree treechildren::-moz-tree-row(out) {
	   background-image: url("row-sent.png") !important;
	   background-position: bottom !important;
	   background-repeat: repeat-x !important;
	}
	#threadTree treechildren::-moz-tree-row(odd,out) {
	   background-image: url("row-odd-sent.png") !important;
	   background-position: bottom !important;
	   background-repeat: repeat-x !important;
	}

The last two clauses (#threadTree) modify the "Zebra striping" colors to make it easier to spot sent messages, but I don't have a convenient way to post the 1KB image files I created.

There are a couple of Thunderbird bugs relating to custom columns (sort order isn't remembered, and you can't modify the text style of a whole row based on the contents of one column), but they're only minor nuisances. They also have nothing to do with the Portable Edition of Thunderbird.

Hope this helps. -hea