(It's possible to use Net::Server to get threading, forking, preforking and so on. Autrijus Tang wrote the functionality and owes docs for that ;)
Merge mboxen. First argument is taken to be the destination mbox, all
# other arguments are asssumed to be source mboxen. If a message doesn't
# have a Message-ID, construct one using MD5. Can read Maildirs as well.
# Uses Mail::Folder::Mbox, which is nominally obsolete. Will optionally
# delete messages older than date (ISO format YYYYMMDDhh:mm:ss) from
# source mbox(en).