sent you may just have to deal with. Many/most programs don't allow sent items to be an iMaped folder. mircosoft only recently allowed users of outlook (starting with 2007) to pick their sent folder thus allowing the sent folder to be seen in multiple places.
syncing every 1 min is going to slaughter your battery life.
One idea does occur to me, though it'll be a little work on your part.
Make a synced folder called Palm sent. After sending the letter (are they called letters

) move it to this folder.
Second option. Always BCC email to yourself.
Deleting from the server when deleted on palm, often depends on the MSP (Mail service provider) it never worked for me with either my earthlink (POP3) or 1and1 (imap) accounts