Hidious mailbox format very common on unix machines.

The format is basically one email message concatenated one after another with a line that starts with "From " seperating them.

This of course means that every message that contains the text "From " at the beginning of a line must be altered. Sigh.

Also mboxes get very slow to parse when they start getting large. many programs (such as pine(1)?) read the entire mbox into memory to parse it. if sizeof(mbox)>sizeof(memory) you're going to be there a while.

A much nicer format is MailDir.