I’d also like to strongly suggest that at least some sort of warning be shown next to “Settings / Account / Sending Mail: Upload sent messages” if “Settings / Account / Folders: Sent folder” is set to None (as it is by default). There is no conceivable scenario where someone would enable a setting to upload sent messages but want them to get uploaded directly to /dev/null.
There are numerous threads and testimonials where this silent pitfall has caused a large amount of confusion or possibly serious stress for users: