We highly recommend creating a "Sent Archive" folder on your primary computer. This is even more obvious on mobile devices like the iPhone. Storing all your sent messages on the server is great for synchronization and easy access from all your devices, but as the Sent folder gets larger, your mail applications will begin to slow down when accessing it.
When you find how to do it for your mail program that is not listed here, send over the instructions so we can post them for others to use! Performance Note Look for similar options for controlling the Sent mailbox behaviour in the mail application of your choice. Instructions for synchronizing your IMAP folders can be found in the Microsoft Office Help Documentation by clicking here. The BlackBerry 10 OS will auto configure your sent folder for synchronization, however if you're using it with Outlook, you may need force Outlook to Synchronize folders to get things working properly with your BlackBerry 10 device. Select "Choose an existing folder." if it's not already selected, then ensure that the Sent folder you want Outlook to use for Sent messages is selected in the list.Choose the "More Settings" button at the bottom of the newly opened window.Select the email account for which you wish to adjust the Sent folder, then choose the "Change" button.Go to the Email Tab if it's not already selected.Select the Tools menu, then choose "Account Settings".
It should *not* be under the "On My Mac" header, since that's an offline folder.
Mac OS X 10.12 Sierra (Directions should be very similar for newer versions of Mac OS X) Follow the directions here to ensure you have selected the "Sent" mailbox on the server as the correct place to store Sent messages.Close the Preferences window and choose to save your changes if prompted."Store sent messages on the server" should be checked.Select the "Mailbox Behaviours" tab on the right.Choose the "Accounts" Tab at the top, then select the account you wish to adjust in the list on the left.Open Mail and choose the "Mail" menu in the upper left.Mac OS X 10.6 - 10.11 (Directions should be very similar for older versions of Mac OS X) Ensure that the folder called "Sent" is checked off under the "On the Server" section.Under Mailbox Behaviours, tap on "Sent Mailbox".(NOTE: If it says POP, then you have to delete the account and re-add it as an IMAP account).