"Obsessive", moi?

For JohnInKansas, the increase in size for individual files compared to mailboxes would most likely be due to the filesystem allocation blocksize. For more modern Windoze systems, that's 4096 bytes, so any individual file will be as many multiples of that as are needed to fit the data. Each file will "waste" on average half that, or 2048 bytes. It can add up to a lot. A file with lots of messages in it may waste a few bytes between messages, but otherwise pack the messages in without fragmentation.