This applies to Apple Mail on OS X as well as the mobile Mail application on iPhone, iPod Touch and iPad. It will also apply to any mail application that cannot auto detect the IMAP Path prefix. If you are seeing this problem on an unnamed mail client, you can assume that the solution described here will work for you, but you will need to do a little legwork to find where the option resides in your program.

As described in our email configuration articles, you will need to set your IMAP Path Prefix to INBOX to solve this problem. Make sure you use all capital letters.

On OS X:

1. Open Apple Mail
2. Open Preferences (Mail menu -> Preferences)
3. Click on the Accounts button along the top and choose the account you have configured
4. Choose the Advanced tab
5. Set IMAP Path Prefix to INBOX
6. Close the preferences window and choose to save the settings.

On iOS4:

1. Open the Settings app
2. Choose Mail, Contacts, Calendars then the account you are configuring
3. Choose Account Info
4. Scroll to the bottom and choose Advanced
5. Scroll to the bottom and set the IMAP Path Prefix to INBOX
6. You may also set the Drafts, Sent and Deleted mailbox to their corresponding boxes

The steps to do this will be very similar on previous version of iOS for the iPhone, iPod Touch and iPad.