Well done for finding a solution! If the IMAP server supports URLAUTH and the SMTP server supports BURL and there is a sent folder detected on the IMAP server then the N9 should upload the message directly to the sent folder on the IMAP server and access it from the SMTP server using BURL. This avoids sending every message twice (once to the SMTP server, and again to the IMAP sent folder) which is normally necessary when using IMAP/SMTP and a sent folder on server. However there appears to be a logic bug in the client so that if (the IMAP server supports URLAUTH or [wrong should be and] the SMTP server supports BURL) and there is a sent folder detected then an attempt to use BURL is made. I've reported this bug, with a suggested fix. Won't be fixed in 1.1, hopefully next release after that.