I decided to make the switch from Entourage (2004) to Mail.app, and I've run into something strange after doing the import. After importing all my messages successfully, I was unable to read any of them in the Import folder. They'd all give me the message:
The message from person ABC concerning “XYZ” has not been downloaded from the server. You need to take this account online in order to download it.
Figuring the Import folder to be the cause of the problem, I moved the imported messages (in a nested folder structure) into a new "Filed Mail" folder I created.
Here's the funny thing: messages in folders in the first level of the hierarchy are readable (e.g. in Filed Mail -> Client X). But messages further down the hierarchy (e.g. in a folder named Filed Mail -> Photo Clients -> Client Z) still show the above message. If I move the folder into the first level (directly into the Filed Mail folder) they become readable, and stay readable even after I nest their folder further down the tree again.
What gives? Looks like Mail.app will only read messages into its database if it sees then in the top 2 levels of folder structure, and ignores anything deeper...
Martin.