mbox files are just text files, however you should take care to not modify it while new mail is coming in. If you have the Procmail utilities (formail et al.) then
lockfile -ml while you work on the file and
lockfile -mu when you're done.
I would advise you to practice on a copy of the file until you see that what you have is working, then take a big gulp and do it on the live file.
Take care not to remove the message separators, each message should start with a "From " line (that's right, From with a space, not a colon, after it). To remove the oldest messages, just remove everything up to just before the first "From " line you want to preserve.
I really have to take exception with your way to
bump your post and to direct it to me personally.
