[kern417]

It could be 2 things

If you're sending emails from you phone, you have to go to Menu>Tools>Options click on the message tab on the bottom and check the box 'keep copies of sent items in Sent folder'

As far as syncing sent items from your gmail account (not sure about the rest, but i use gmail and this worked for me) you have to go to Menu>Tools>Manager Folders and check the 'Sent Items' folder so that it will sync those messages at the same time as your inbox. This also works for any labels/filters that you have in Gmail, but the only folder it syncs automatically is the Inbox. I have filters for Facebook and my work from Home Job so I had to select those boxes to get the filtered emails to my phone

hope this helps