Or, How I reclaimed 1.25 gigabytes of my hard drive.

When 10.4 imported mail from the old 10.3 mbox files, it broke each message into an individual file so Spotlight could index them. The old mbox files, rightly, were left on the drive. For most people this wouldn’t take up a noticeable amount of space, however those of us with a ton of mail saw a significant hit to our disk space.

The following commands will remove the unused mbox files from the drive, recovering a potentially large amount of disk space:

    cd ~/Library/Mail
    find . -name "mbox" -ls

Make sure the only thing listed are mbox files in your mail directory (they should be). To delete all those files, change the last “-ls” of the above command to “-delete“. (I didn’t include the full command on purpose since it deletes files and I wanted to strongly encourage everyone doing this to check the file list before deleting.) Just to be doubly safe, backup before doing this.

Total size of my mail folder went from 3.07 GB (3,206,511,328 bytes) to 1.84 GB (1,884,864,581). A savings of almost 1.25 GB. At $229.00 for a 93.2 GB formatted notebook drive, that’s an actual cost savings of $3.02.

Note there was/is a bug with Mail importing under 10.4 where very large mbox files don’t read correctly. Make sure all your messages really did import correctly before deleting your mbox files.