Family tech support means migrating email so an old machine can be disposed of. In this case, from a very old Outlook Express 5.02 running on Mac OS 9.2 to Apple Mail on Mac OS X. I went via Eudora, which is available for old and new Mac OS.
Rather than setting up networking, I used Target Disk Mode to copy over software and data.
Download Eudora 6.1.1 (Classic) from Old Eudora Installers and install it under Mac OS 9. Open Outlook Express and make sure your inbox is empty: folders will be converted, but the inbox wasn’t, so move its contents into folders. Launch Eudora and import the identity from Outlook Express. This import is the longest part of the process. Apart from ignoring the inbox, the folder structure also changes slightly; folders after the conversion that contained messages directly will now have them moved to another subfolder named after the parent folder.
Copy the Eudora Folder from Documents on the old hard disk to the new machine.
Install Eudora Mailbox Cleaner (I used 4.9) and drag the copied Eudora Folder onto it. This will do a full migration to Apple Mail including attachments.
Under Mac OS X, we could also install a more recent version of Eudora and simply use the copied Eudora Folder.
Entourage runs under Mac OS X and used to import from Outlook Express circa 2004 but dropped support in later releases.
Entourage and Apple Mail both offer a Eudora import but both ignore attachments.
As an extra twist, Eudora Mailbox Cleaner is a PowerPC application, so it won’t run under Mac OS X 10.7 now Rosetta has been removed. If your email is sitting in proprietary software released over ten years ago then consider your exits carefully.