Outbox
When you wrote a message and click on "Send" that message is sent immediately to the server. If you're not connected at this time and like to send the message later, you can click "Save" instead to send the message to the Outbox where it patiently waits for your next online session. Open the Outbox to see the waiting messages. When you're online, choose "Article | Send Messages" to restart the sending process.

Sent
This command opens the Sent folder which holds copies of your own postings. View your messages manually or search them by using Group | Find (select "Search in Bodies" there). This only works when the Sent folder is already opened. Alternatively you can use "Special | Search in Folders". Don't forget to put a checkmark beneath "Sent" there.

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Archive
This lets you create a new folder where you can store postings. Usually you transfer messages with "Transfer | [Archive-Folder name] "or "Article | Archive [Archive-Folder name]"

Queue
Create a new Queue folder with this command. Unlike the regular (archive) folder, a queue folder stores only the headers when you transfer articles into it. Then when you read or decode the articles, Xnews gets the articles from the server, just as if you're in a newsgroup.
See the Xnews manual (Folders, section) for more info about queues.
To use the queue, transfer messages with "Transfer | [Queue-folder name]" or "Article | Q-Archive [Queue-folder name]".