Changing the Sent Items folder in OS X Mail

We have a linux IMAP server that uses “Sent” as the default name for it’s Sent Items folder. However, at least in my case, the OS X Mail app seemed to expect the folder to be called “Sent Items”.

To set the Sent folder to be pointed at the correct Sent Items folder, you must select that folder from the account tree, and then select Mailbox > Use This Mailbox For > Sent.

It took me a while to work this out, so I have posted here for future reference.